Evolution multiple choice question

1. Male birds of different species sing species-specific songs to attract mates. Females only mate with males that sing their species-specific song. This is an example of


A. temporal isolation.
B. post-zygotic isolation.
C.reinforcement.
D. pre-zygotic isolation.

Answer : D
2. New species can form through allopatric or sympatric speciation. Which of the following mechanisms will act more strongly on populations that are initially separated in allopatry than on those initially separated in sympatry?

A. genetic drift
B. disruptive selection
C. gene flow
D. reinforcement

an explanation for each answer would be nice