You can't fancy what great trouble they have _______ the problem ________.[ ]

A. to solve; being discussed   

B. solving; discussing

C. to solve; to discuss  

D. solving; being discussed

食堂购进200斤含水量为90%的西红柿，3天后再测试发现西红柿的含水量变为80%，那么这批西红柿的总重量共减少了( )千克。

A．100
B．10
C．20
D．50