Question

8a. Since American Idol premiered on television, many talented contestants have appeared on the show.
8b. Since American Idol premiered on television, many talented contestants appeared on the show.
my answer is A. please give me an explanation on the chosen answer, thanks

Answer 1

A is correct.

See the reasons for the differences between simple past tense and the perfect tenses:
http://grammar.ccc.commnet.edu/grammar/tenses.htm

Answer 2

thanks