Wiesel said that the Holocaust "happened yesterday or an eternity ago" to (a.) to show that he remembers the Holocaust clearly and always will. Wiesel meant that the memories from the Holocaust were very strong that he can never forget those who suffered.
C. Bill raced after the ball and threw it back to Cheryl.
Answer: Compound
Explanation:
A compound sentence consists of two or more independent clauses joined with a comma and coordinating conjunction, also known as the FANBOYS (for, and, nor, but, or, yet, so).