A split infinitive is an infinitive that

A. has a word between "to" and the verb.
B. is used as an adjective or a noun.
C. is used without the word "to."
D. must have a subject

..A?

Each one of the following sentences contains a clause. In which sentence is the clause used as an
adverb?
A. All of the delegates who have actual opinions should keep silent.
B. Whales, which eat krill, prefer colder ocean waters.
C. What you really need is a back massage.
D. I do not mind fishing, as long as I don't have to bait the hook.

...D?

Yes.

I expect to completely recover within a week or two.

For the first question, you are correct. A split infinitive is an infinitive that has a word between "to" and the verb. In the given options, option A states this correctly.

For the second question, the correct answer is not option D. Let me explain how to identify a clause used as an adverb. An adverb clause modifies a verb, adjective, or another adverb in a sentence. It typically answers questions like "how," "when," "where," "why," or "under what conditions." In the given options:

A. "who have actual opinions" modifies "should keep silent", not a verb, adjective, or another adverb.
B. "which eat krill" modifies "prefer colder ocean waters", not a verb, adjective, or another adverb.
C. "What you really need" modifies "is", not a verb, adjective, or another adverb.
D. "as long as I don't have to bait the hook" modifies "do not mind fishing", which is a verb.

Therefore, the correct answer is D. In option D, the clause "as long as I don't have to bait the hook" is used to describe under what conditions the speaker does not mind fishing.