It is quite easy to cheese the problems: many of them don't look like word definitions ("a sharp pain in the back"), many problem have this "correct answer + opposite meaning + 2 unrelated things" answer structure, and for the second half of the answers, very often the longest answer is the correct one. The wrong options are not well designed here.
The sample of words is also heavily biased towards concepts relating to words, speech, speakers, and/or persuation. They are likely generated by an LLM which is primed on the task of choosing words, and end up choosing words related to "words".
For context, I'm an L2 speaker, linguistic nerd, and I use English mostly in academic/professional settings. I got 75,400 by a combination of the tactics above; in reality it might be closer to 10-15k.
The design is also painfully similar to Duolingo if anyone can spot that.