Question

a hummingbirds wings beat 80 times per second, while an eagles wings beat 2 times per second. which bird produces a higher - pitched sound?
the hummingbird, because its wings vibrate faster
the eagle, because it is larger
they produce the same pitch
neither bird produces sound with wing beats

Explanation:

Pitch is related to the frequency of vibration. A higher - frequency vibration (more vibrations per second) produces a higher - pitched sound. The hummingbird's wings beat 80 times per second, while the eagle's wings beat 2 times per second. Since the hummingbird's wings vibrate faster (higher frequency), it will produce a higher - pitched sound. The size of the bird (as in the case of the eagle being larger) is not directly related to the pitch of the sound produced by wing beats. And clearly, their wing beats do produce sound (so the option about neither producing sound is wrong), and they don't produce the same pitch because their vibration frequencies are different.

Answer:

The hummingbird, because its wings vibrate faster.