补充材料--339，318

339. Acid rain and snow reslult from the chemical reactions between industrial emissions of sulfur dioxide and nitrogen oxides with atmospheric water vapor to produce highly corrosive sulfuric and nireic acids.

A)with atmospheric water vapor to produce highly corrosive sulfuric and nireic acids

B)with atmospheric water vapor producing highly corrosive sulfuric and nireic acids

C)and atmospheric water vapor which has produced highly corrosive sulfuric and nireic acids

D)and atmospheric water vapor which have produced sulfuric and nireic acids which are highly corrosive

E)and atmospheric water vapor to produced highly corrosive sulfuric and nireic acids

答案E，怎么不是C呢？

318 New techniques in thermal-scanning photography, a [rocess that records radiation from surface areas, makes it possible to study the effects of calefaction, or warming, of a river in greater detail than ever before.

A)makes it possible to study the effects of calefaction, or warming, of a river in greater detail than ever before

B)make it possible to study, in greater detail, the effects of calefaction, or warming, of a river than ever before

C)have made it possible to study in greater detail than ever before the effects of calefaction, or warming, of a river  

答案是C，为什么要用完成时呢？为什么不选B？

谢谢了！！