Glaciers can only form when a. there is an ice age. b. there is a u-shaped valley in the mountains. c. the amount of snow exceeds the amount of rain. d. more snow falls than melts

D. is correct.
A glaciars formation does not depend on an ice age, nor does it depend on a U shapes valley, nor does rain interfere in its formation.

For a glaciars to be formed we'll just need a large amount of snow accumulating on a surface.

Hope it helped!

D is correct 

                  ps hit that red heart down below

Lacking something of the ozone layer