What must you do when carrying a baby in a rear-facing baby seat in the passenger seat?

Answer: C — Deactivate the passenger airbags

When carrying a baby in a rear-facing baby seat in the passenger seat, the passenger airbags should be deactivated. This is because if the airbags were to deploy in an accident, it could seriously injure or even kill the infant. Option A and B are not necessary and do not address the safety concern for the baby. Option D may seem like a viable option, but it does not address the risk of airbag deployment. It is important to follow the correct safety precautions for transporting infants to ensure their safety.