hello!
let's go through all of these words' definitions.
u-shaped valley - where the valley curves down like a u shape
corrie - similar to the hole created at the top of a volcano when it erupts, it's almost like a dent in a mountain
pyramidal peak - a mountain where the peak is very sharp, such as the matterhorn.
arete - two valleys separated by a thin mountain range
i'm going to assume you know how to read a topographic map, but in case you don't, feel free to comment.
now, let's figure out which one's which:
a - seems to be a mountain range separating two valleys, with a mountain running from top center to bottom center and two valleys on either side. therefore, i'd consider this an arete.
b - it looks like a dent into the mountain, like what a corrie is.
c - looks to be a valley, with two steeper sides curving up around the bottom of the valley which has a river in it. i would consider this an u-shaped valley.
hope this !