how does the contrast between an object and the background in a picture affect the appearance of depth?

a. The greater the contrast, the flatter the appearance
b. The more objects there are, the more contrast there will be.
c. The closer in tone, the flatter the appearance
d. the contrast has no effect on the appearance of depth.

I think it is B. the more objects there are, the more contrast there will be.
Is that right?