Allen’s new job paid twice as much as he had made ______ in the small restaurant. [ ]

A. working

B. worked

C. to work

D. when worked

用于核移植的受体细胞一般都选用[ ]

A．受精卵

B．MⅠ期卵母细胞

C．MⅡ期卵母细胞

D．红细胞