D
Below is a question with multiple-choice answers. Choose the correct option based on your reasoning.

### Question:
Based on the Doppler effect, the electromagnetic waves reaching Earth from a galaxy that is moving away from Earth would be expected to

### Choices:
A. experience an increase in their amplitude.
B. experience an increase in frequency.
C. experience a decrease from transverse waves to longitudinal waves.
D. experience a decrease in frequency.

### Answer:
