We saw him（）the white building and go upstairs.
A. enter
B. entering
C. to enter
D. entered
The discharge head of a centrifugal pump will vary directly with the （）.
A. change in impeller diameter
B. square of the impeller diameter
C. cube of the impeller diameter
D. impeller efficiency for large changes in the size of the impeller
组成岩浆岩的矿物有哪些？其中哪些属于浅色矿物，哪些属于深色矿物？
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