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
If you've ever frozen mid-sentence wondering whether to say an information or some information, child or children, they or them — you've hit the core of how English uses nouns. Nail this down and articles, plurals, possessives, and pronoun choice all stop feeling like guesswork.
A noun is a word that names something: a person, place, thing, idea, action, or quality. Nouns are the building blocks every other part of speech bolts onto. Spot one in a sentence and you can usually predict the article, the verb form, and the pronouns that follow.
Possessive
If you've ever stared at its and it's and not been sure which one belonged in your sentence, you've met English's most-confused possessive. The fix is small but immediate: its (no apostrophe) is the possessive of it; it's (with apostrophe) always means it is or it has. Get this right and you instantly look more careful as a writer.
The possessive form shows ownership in English. Most nouns take 's (Sarah's book); plural nouns ending in s take just an apostrophe (students' essays). Pronouns have irregular possessive determiners (my, your, his, her) and pronouns (mine, yours, his, hers).
English Grammar Basics
If grammar feels like a tangle of rules you can never quite remember, the fix isn't more advanced material — it's making the foundations automatic. The English Grammar Basics tag is where you do that: the building blocks every other topic stands on. Get these right and the rest stops feeling random.
It marks quizzes and explainers covering the core of English: nouns, verbs, adjectives, adverbs, prepositions, conjunctions, tenses, voice, mood, and basic sentence structure. Useful whether you're a beginner or refreshing rusty knowledge.
Humor
If you've ever reached the third drill of present perfect and felt your eyes glaze over, you've hit the limits of dry repetition. Practice that's even mildly funny is far easier to come back to — and far easier to remember weeks later. That's the whole point of the Humor tag.
The Humor tag marks questions where the author has tried to make the practice entertaining alongside instructive. Subjective, sometimes silly, but designed to keep you engaged long enough for the rule to stick.
B2 | Upper Intermediate
If a university admissions team or visa office has ever asked you for an English test score, B2 is probably the level they had in mind. It's the threshold where your English stops being a constraint and starts being a tool — and the line between B1 and B2 is often the line between "stuck in beginner classes" and "ready to study or work in English."
B2 is the upper-intermediate level in the CEFR framework, demanding flexible control of mixed conditionals, passive voice across tenses, reported speech with backshifting, and participle clauses.
Difficulty: Medium
If easy questions feel too obvious but hard questions leave you guessing, you're probably ready for Medium — the level where most real learning happens. It pushes just enough to expose the rules you don't quite have yet, without burying you in edge cases. This is where steady fluency is built, one well-aimed challenge at a time.
The Medium difficulty tag marks middle-range challenges — typically A2 to B1. One rule per question, realistic distractors, and contexts that require active thought rather than instant recognition.