【正确答案】 B

【答案解析】解析：本句话的意思是：厚厚的云朵遮住了月亮。prevent：预防、阻止。例如：These rules are intended to prevent accidents．这些规则旨在防止事故发生。hold：持有、保留。例如：He always holds a pipe between the teeth．他嘴里总叼着烟斗。darken：使模糊、变黑。例如：We darkened the room by closing the shutters．我们关上百叶窗．使房间变暗了。blacken：使变黑、诽谤。例如：The smoke had blackened the white walls of the house．烟把房子的白壁熏黑了。