PREDICT Why do you think energy must be added to change carbon powder into a
synthetic diamond?

Explanation:

Energy must be added to change carbon powder into synthetic diamond because at ordinary temperature and pressure conditions, this reaction will not take place.

To form diamond, conditions of high pressure must be made available. Diamond is an allotrope of carbon that is very hard and difficult to break.

To form diamond synthetically, we must be able to replicate the natural conditions by which it forms.

Diamond forms under very high grade metamorphic pressure. This must also be the condition to form the synthetic variant.

the answer your looking for is c).