The correct answers are brother-in-law's and sisters-in-law.
Brother-in-law's is a singular possessive. To show possession for a compound noun, you always add 's to the very end of the word, regardless of where the head noun is.
Sisters-in-law is a simple plural. Because there are "three" of them, we need the plural form. We pluralize the head noun (sister -> sisters) without adding an apostrophe.
Noun
A noun (from Latin nōmen, literally meaning "name") is a word that functions as the name of some specific thing or set of things, such as living creatures, objects, places, actions, qualities, states of existence, or ideas. Linguistically, a noun is a member of a large, open part of speech whose members can occur as the main word in the subject of a clause, the object of a verb, or the object of a preposition.
Lexical categories (parts of speech) are defined in terms of the ways in which their members combine with other kinds of expressions. In English, nouns are those words which can occur with articles and attributive adjectives and can function as the head of a noun phrase.
Possessives
In English, possessive words or phrases exist for nouns and most pronouns, as well as some noun phrases. These can play the roles of determiners (also called possessive adjectives when corresponding to a pronoun) or of nouns.
For historical reasons, this case is misleadingly called the possessive (case). It was called the genitive until the 18th century and in fact expresses much more than possession. Most disagreements about the use of possessive forms of nouns and of the apostrophe are due to the erroneous belief that a term should not use an apostrophe if it does not express possession.
In the words of the Merriam-Webster Dictionary of English Usage:
The argument is a case of fooling oneself with one's own terminology. After the 18th-century grammarians began to refer to the genitive case as the possessive case, grammarians and other commentators got it into their heads that the only use of the case was to show possession. ...
This dictionary also cites a study in whose samples only 40% of the possessive forms were used to indicate actual possession.
Nouns, noun phrases, and some pronouns generally form a possessive with the suffix -'s (apostrophe plus s, but in some cases just by adding an apostrophe to an existing s). Personal pronouns, however, have irregular possessives, and most of them have different forms for possessive determiners and possessive pronouns, such as my and mine or your and yours.
Possessives are one of the means by which genitive constructions are formed in modern English, the other principal one being the use of the preposition of.
English Grammar Basics
"English Grammar Basics" tag marks quiz and explainers that intend to provide a solid foundation in English language grammar. This includes all the major concepts and topics in English grammar, including nouns, verbs, adjectives, adverbs, prepositions, conjunctions, tenses, voice, mood, and sentence structure. The explanations we provide in quiz intro sections are clear and concise, making it easy for learners of all levels to understand. These quizzes are designed to be fun and engaging, helping you to retain the information more effectively. Whether you're a beginner or looking to refresh your knowledge, look for content marked with the "English Grammar Basics" tag for everything you need to master English language grammar.
Humor
Humor is subjective, but at least the author tried.
B2 | Upper Intermediate
B2, or Upper Intermediate, is the fourth level on the CEFR scale. It marks the point where you move from "getting by" to genuinely comfortable communication — handling complex topics, expressing nuanced opinions, and understanding most of what you read or hear in real-world contexts.
What a B2 user can do
At this level, you're expected to:
- Understand complex texts on both concrete and abstract topics, including technical discussions in your own field.
- Follow extended speech and lectures, even when the structure isn't entirely clear, as long as the topic is reasonably familiar.
- Interact fluently and spontaneously enough that conversations with native speakers flow naturally — without strain on either side.
- Produce clear, detailed text on a wide range of subjects, using connectors and cohesive devices to build well-structured arguments.
- Explain and defend a viewpoint on a topical issue, weighing the advantages and disadvantages of different options.
- Recognize implicit meaning — reading between the lines in demanding, longer texts.
What B2 grammar looks like in practice
B2 is where grammar stops being about isolated rules and starts being about flexibility and precision. You're expected to control structures like:
- Advanced conditionals and mixed conditionals — moving beyond simple if-clauses to express hypothetical and counterfactual meaning.
- Passive voice in varied tenses and contexts, not just present and past simple.
- Reported speech with correct sequence of tenses, including backshifting and reporting verbs.
- Participle clauses and the distinction between participles and gerunds.
- Comparative and superlative structures beyond basic -er/-est, including double comparatives and qualifying expressions.
Errors still happen at B2, but they rarely cause misunderstanding. The goal is controlled, flexible use of language across social, academic, and professional settings.
How B2 fits in the CEFR progression
B2 builds directly on the foundations of B1 (Intermediate) and prepares you for C1 (Advanced). Many university entrance exams, professional certifications, and immigration requirements target B2 as the minimum standard.
Self-check: If you can read a newspaper editorial, follow most of a TED talk without subtitles, and write a clear essay arguing a position — you're likely operating at B2.
Ready to test yourself? Try Is your English level B2/Upper Intermediate? or practise specific B2 grammar with challenges like Basics. Advanced Conditionals And "wish", Basics. Passive Voice, and Sequence of Tenses in Indirect Speech.
Difficulty: Medium
Medium difficulty. Difficulty levels represent author's opinion about how hard a question or challenge is.