题目

在观察装片时，由低倍镜换成高倍镜，细胞大小、细胞数目、视野亮度的变化是    A．变大、变少、变暗                 B．变大、变多、变亮           C．变小、变多、变暗                 D．变小、变多、变亮 答案：AThe students didn't stop talking _______ the teacher came in. [     ]A. before B. until C. when D. because