The correct option is C Has finished
In this sentence, the usage of 'everybody' implies singular pronoun. Singular pronoun uses 'has', instead of 'have (used with plural pronouns). Moreover, the sentence is in present perfect tense (it
is used to indicate an action which started in the past and has continued up
untill now). So, the correct usage is 'has finished'. If the sentence would have in past perfect (it
is used to indicate a completed action of the past that happened before another
event took place), then 'had finished' should have been used. Past simple (finished) indicates
an action that has already been completed.