The ground is wet. Yes, didn't you know? for the last 20 minutes.
A. It's raining
B. It was raining
C. It's been raining
D. It has rained
网友回答
A. It's raining
B. It was raining
(答案→)C. It's been raining
D. It has rained
解析：时间状语for the last 20 minutes，表示的是过去的一段时间里完成的动作持续到现在并有可能继续下去，动词的时态应用现在完成进行时。故选C。