Why does a siren have a lower pitch as it moves away from you? A The period of the sound wave is decreased B The amplitude of the sound wave is increased C The crests of the sound wave are farther apart D The troughs of the sound wave are spaced closer together.

it is letter C

there is a video explaining this

C

Explanation:

I think it's C because when it moves further away the sound wave is moving apart  

concave lenses are used here. they spread the light out before it reaches the convex lens in the eye, therefore letting the image focus directly on the retina. hyperopia is known to you probably as farsightedness.