Question

They could not meet the officer-in-charge (change in voice)
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Answer 1

Explanation:

The officer-in-charge can't meet them.

Here, could will be change to can, and not will remain same. I just used can't to substitute it.

They will be changed to them. The officer in charge will become the subject.

This is a change of passive voice to active.

Answer 2

Answer:

The officer-in-charge could not be met by them.

Hope it helps.