牙周膜内的上皮剩余来源于
A．牙板上皮B．前庭板上皮C．缩余釉上皮D．上皮根鞘E．口腔黏膜上皮
参考答案：D
—Dad, please tell me when Mum_____. I miss her very much.
—She will return when she_____ her task. And she will bring a nice present for you.
A．returns; finishes
B．returns; will finish
C．will return; finishes
D．will return; will finish
观察如图所示，回答问题
（1）图中所示的是什么历史重大事件？
（2）此事件发生于什么时间？
（3）标志着什么？
