In the hot afternoon after a long walk, I rested under the shadow of a tree.

Options

A. shelter
B. shade
C. cool
D. No Improvement

Answer

B

Explanation

(2) shade (Noun): an area that is dark and cool under or behind something. (tree, building, etc.)
shadow (Noun) : the dark shape that somebody I something forms on a surface, when he/it is between the light and the surface. Here, shade is the right usage.