"How's the baby?"

问题描述:

"How's the baby?"
"He's generally healthy,but every now and then he__________cold."
a)has caught
b)is catching
c)will catch
d)does catch

选D
every now and then 是时常、经常的意思,跟usually类似,应该用一般现在时.
不过题目还是有一点点小问题,感冒是catch a cold,冠词a一般不能省略.