It was in the factory ________ his friend worked ________ he picked up a lot of experience.  [ ]

A. where; where        

B. that; where  

C. that; that        

D. where; that

有渣口的高炉，上渣率一般要求在（）。

A.大于50%

B.100%

C.大70%

D.大于30%