Identify the sentence with correct use of the conditional perfect tense:
A. If they had arrived earlier, they could have met the author.
B. If they arrived earlier, they could meet the author.
C. If they have arrived earlier, they could meet the author.
D. If they arrive earlier, they could have met the author.
The correct form is "If they had arrived earlier, they could have met the author," using the conditional perfect tense for an unrealized condition in the past.