There are two exits in the dog and mouse hole, one is flat and the other is a raised mound. Air with the same mass passes through the upper surface of the outlet at the same time, and the wind blowing through the plane has low speed and high pressure. The wind blowing over the raised surface has high speed and low pressure. As a result, the wind on the ground blew into the caves of dogs and mice, bringing cool wind to dogs and mice. To sum up, it can be seen that the airflow should flow in from the flat hole and out from the hole of the uplift hill. Therefore, only A meets the question.

So choose a.