The correct answers are: I have lived in this gloomy castle for 400 years. I haven't seen the sun since 1893. I have been practicing my smile for the last few days.
Use for to express a duration or period of time (for 400 years, for five centuries, for a long time).
Use since to refer to a specific starting point in the past (since 1893, since Monday).
Preposition
Preposition vs particle: same words (in, on, up, off), different jobs. A preposition links to a noun (look at the book). A particle changes verb meaning without a noun (give up = quit). Test: is there a noun/pronoun after it forming a prepositional phrase? → preposition. Does it change the verb's meaning? → particle in a phrasal verb.
A preposition = small word connecting a noun to the sentence (time, place, manner, relationship). Choice is idiomatic per verb/adjective combination.
Diagnostic: struggling with which preposition to use? It's almost never about logic — look up the specific verb/adjective + preposition combination.
Perfect tense
Present perfect vs simple past: I lost my keys (past: specific time, done). I have lost my keys (perfect: result matters NOW — I still don't have them). The perfect always connects past action to present relevance. If the time is specified (yesterday, in 2010) → simple past. If the result matters now → present perfect.
The perfect aspect = have + past participle. Marks completion relative to a time point. Three forms: present/past/future perfect.
Diagnostic: does the sentence mention a specific finished time (yesterday, last year, in 1999)? → simple past. Is it about the result/relevance NOW? → present perfect.
Humor
Humor vs serious practice: both teach the same rules. The difference is engagement — funny material keeps you coming back and creates stronger memory hooks. If dry drills bore you into quitting, humorous practice is more effective because you actually do it.
The Humor tag filters for entertaining practice: silly contexts, wordplay, absurd examples — all testing real grammar rules underneath.
Diagnostic: if you find yourself dreading practice → try filtering by Humor. If you're preparing for a formal exam and want serious register → filter it out.
B1 | Intermediate
B1 vs B2: B1 handles standard everyday communication and simple opinions. B2 handles abstract topics, sustained arguments, and nuanced register. If you can chat about your life but struggle to debate an issue or write a formal essay, you're B1.
B1 is the intermediate CEFR level: independent handling of familiar topics, second conditional, basic passive, reported speech, and linking words for cause and contrast.
Diagnostic: can you read a newspaper article on a familiar topic and summarise the argument? Comfortably → B2. Struggle with abstractions → still B1.
Medium
Medium vs Easy: Easy has one obviously correct answer and clearly wrong distractors. Medium has one correct answer but plausible distractors — you need to actually know the rule, not just guess from sound.
The Medium tag filters for A2–B1 challenges with realistic difficulty: one rule per question, plausible alternatives, everyday contexts.
Diagnostic: if you're scoring 90%+ on Easy, move here. If you're below 60% on Medium, go back to Easy for that topic. Target 70–80% accuracy for maximum learning.