下列各项中属于口腔上皮细胞的是[ ]
A．
B．
C．
D．
答案：D
I __________get on the bus when I heard someone calling me from behind.
A．was to
B．was going to
C．would
D．was about to
比较腔肠，扁形和环节三门动物，说明有机体结构和功能方面的进化
