After a short break he went on _____. [ ]
A. to speak
B. speak
C. speaking
D. spoken
答案:C
钙质原料主要提供材料组成所需的()。
A、CaCO3
B、CaO
C、SiO2
D、Al2O3
励磁机是供水轮发电机()励磁电流的。
A.定子;
B.转子;
C.永磁机;
D.辅助发电机;