Can you give some information , what book?
Hm, are you sure you got the question right? Because all of the sentences are written in active voice! Active voice is essentially everything that is not in the passive voice, and I don't see any passive voice here.
Passive voice would be formed with subject+form of "to be" + past participle,
and we have no example of this. All of the sentences here are in active voice.
The answer is <span>A. Several of the speakers suggested that much remained to be done.
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