问题
选择题
Usually, a mother wolf gives birth to five to seven baby wolves .
A．for a time
B．for the time
C．at the time
D．at a time
答案
答案：D
题目分析：句意：通常，一个狼妈妈一次生了五到七的狼崽at time是偶尔的意思；at a time指每次；for a time是暂时及一段时间的意思for the time是在当时。根据题意故选D.
