人口过程
参考答案：指人口生存、变动与发展过程，是这一过程的概括。
---I will have to think about it again．
--- If you _ , you may lose the opportunity to compete altogether．
A．hesitate
B．wonder
C．continue
D．fail
心脏的正常起搏点是
A．窦房结
B．右心房
C．房室交界
D．心室肌
E．浦肯野纤维
