The function of the bypass valve on the self-contained breathing apparatus is to（）.

A.control the pressure of the oxygen as it enters the body

B.allow the wearer to manually give himself oxygen

C.release excess heat which would otherwise cause the bottle to explode

D.allow exhaled gases to pass outside the bottle

按照外商投资企业和外国企业所得税法的规定，下列企业不属于“生产性外商投资企业”的是( )。

A．石油、天然气开采企业

B．制药工业

C．农业企业

D．建材工业