Question

horses and donkeys can mate, but they produce a mule, which is always a sterile animal. this means that they cannot produce viable offspring and are isolated.

Explanation:

Reproductive isolation occurs when two species cannot produce viable, fertile offspring. In this case, horses and donkeys produce a sterile mule, which is a key characteristic of reproductive isolation. Geographical isolation involves physical separation (not relevant here). Temporal isolation is about different breeding times (not mentioned). Behavioral isolation is about different mating behaviors (not the issue here).

Answer:

reproductively