A small puzzle to prove you are a person. Failing it again and again usually means your connection looks suspicious to the site, not that you are answering it wrongly.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a bouncer asking a question a machine can't answer.
For example
You are asked to pick every square with a bus in it, three times. You are not answering wrongly. Your connection looks odd to the site.
This is one card out of 275.
The hundred words you meet most are free — the whole set, animated, in one file that works with no internet.
Volume 1 has all 275 in fifteen chapters, with Staying Safe the largest chapter on purpose.