[单选] The moon was obscured by thick clouds.

题目：[单选] The moon was obscured by thick clouds.
A . held
B . prevented
C . darkened
D . blackened

正确答案：B
解析：句意为：厚厚的云朵遮住了月亮。prevent意为“预防、阻止”，hold意为“持有、保留”，darken意为“使模糊、变黑”，blacken意为“使变黑、诽谤”。obscure意为“遮掩，使变暗”。和B项同义，故选B项。