A pumproom is suspected of accumulating ga

问题：

A pumproom is suspected of accumulating gases after a ventilation machinery breakdown. Where should the combustible gas indicator case be placed when testing the pumproom atmosphere for combustible gases?（）.

A.In the lower level of the pumproom

B.In the middle level of the pumproom

C.In the upper lever of the pumproom

D.On the deck outside the pumproom