To our relief, at last the opening ceremony of the sports meeting we had been looking forward to _____

on time.[      ]

A. had started

B. starting

C. started

D. being started

下列有关地球昼和夜的叙述，正确的是（）

A.晨昏线与经线不可能重合

B.如果没有地球自转就不会有昼和夜的产生

C.地球上昼夜更替现象是一种自然现象，有利于人类的休养生息

D.地球上任何地点一天中昼和夜的时间之和都是12小时