Final answer:
The peregrine falcon's motion can be described as moving with constant speed.
Step-by-step explanation:
The peregrine falcon's motion can be described as b) The falcon is moving with constant speed.
When an object moves with constant speed, it means its velocity does not change. In this case, the falcon flew 680 km in 4 hours, which means its average speed is 170 km/h. Since the speed remains constant, the falcon's motion can be described as moving with constant speed.