Answer:
D. The class gave her many ideas for the project, but she used only one.
The easiest way to find passive voice is by looking for any uses of the word "by", or any form of the verb "to be". In both A and B, the uses of "had been" and "by" are clear indicators of passive voice. In C, the second sentence says "only one was used". "Was" is a past tense form of "to be" and is therefore, passive. Instead of these, you should say that it is the class that is acting (by giving her ideas) and in the second part, that "she" is acting (by using only one). So rather than "she'd been given by" or that "only one was used", D uses active voice, saying that the subject is acting on something instead of something being acted upon by the subject.
Step-by-step explanation: