In which sentence does the prepositional phrase act as an adverb? a. last evening, anne suffered from a headache. b. the door to the attic was left open. c. mr. frank discussed the problem of noise in the annex. d. he bought a drink for mr. dussel

In A, Last evening describes when she suffered, so it's acting as an adverb.
In B, open could describe the door or how it was left, meaning it could be acting as an adjective or an adverb.
In C, in the annex could describe where it was discussed or the problem of noise, meaning it could be acting as an adjective or an adverb.
In D, for Mr. Dussel describes the drink, not bought. (adjective)

A is the only one that must be an adverb, so I'd go with that. It wouldn't be hard to raise an objection with your teacher if you're "wrong," anyways.