The American Toad and the Fowler's Toad Are Closely Related

The American toad and the Fowler's toad are closely related species whose ranges overlap. The American toad mates in the early part of summer, while the Fowler's toad mates later in the season. What type of reproductive isolating mechanism keeps these toads separate species?

A) postzygotic isolation
B) temporal isolation
C) behavioral isolation
D) habitat isolation
E) mechanical isolation