English Language & Usage Stack Exchange is a question and answer site for linguists, etymologists, and serious English language enthusiasts. It only takes a minute to sign up.
Sign up to join this community
Answer the multiple choice questions and fill in the blanks, if known.
Do the words after the comma only refer to the words immediately preceding it? Meaning-- Answer ALL of the questions but only fill in the blanks if you know it. Without the comma, does it mean you only have to answer the questions and fill in the blanks if you know them?
The clause after the comma is ambiguous in that regard: it may modify the whole sentence, and it may modify only the clause after and. We'd need more context to tell which was intended. At any rate, the if clause doesn't seem to add much practical information: of course you will fill in what you know in either type of question. So you might as well ignore it, unless there is something in the context that makes it important.
I think the sentence is asking you to (1) answer all of the multiple choice questions and (2) answer only those fill-in-the-blank questions for which you know the missing piece. This instruction may well be different from the one the writer intended to provide. But, I think that the adjective "known" must apply to the noun "blanks". It's too much of a contortion to apply it to a noun in the first clause, and there's not enough information to assume some understood third noun for it to modify.
