Final answer:
If pregnant sheep are injected with PYY during a critical gestation period, their female offspring will show homosexual behavior.
Step-by-step explanation:
The answer to the question is a. PYY.
When pregnant sheep are injected with PYY (Peptide YY) during a critical gestation period, their female offspring may show homosexual behavior. PYY is a hormone that is primarily involved in regulating appetite and energy balance in mammals. However, its effects on sexual behavior and orientation in animals are still being studied and understood.