曝光时感光中心上聚集了为数很少的（）。
A.卤化银
B.银原子
C.银离子
D.溴化银分子
参考答案：B
肝胆动态显像不包括以下哪个时相（）。
A.血流灌注相
B.静脉血池相
C.肝实质相
D.胆管排泄相
E.肠道排泄相
I ________ sooner but I didn't know that they were waiting for me.
A．had come
B．was coming
C．would come
D．would have come
