Which of the following types of landforms can also be called a “depression” because it is naturally lower than its surroundings?
a. a plateau
b. a valley
c. a mountain
d. a hill

B. a valley

When you see a valley, it normally starts off with a high elevation, but then drops low before curving up again.

my explanation of a valley is horrid, but if you google pictures of a valley you would understand. :)

b. a valley, can be called as a depression and its naturally lower than the surroundings, of a mountain or a hill or the  plateau.

Explanation:

Valley are usually v-shaped rivers and the valleys of the mountains are U-shaped types and thus they are the lowest point of the surrounding areas and hence are lower than the surrounding land masses. The lowest point of the valley can open up to the ocean ore the sea level or valley bottom that has various features formed by the ink and the collapse of the ranges or trench formations. Thus valleys represent the depressed landscapes that have been blown down or reduced by the active geomorphic event and these are activated form the surface above that bring down or lower the base of the landscape like the winds, river water, glacier ice and man himself.

Well, a and b together would be negative. b alone would also be negative.