什么是屏障避孕？
参考答案：
是通过物理性阻隔和化学性杀灭精子活性，使精子和卵子无法相遇，起到避孕作用。
---What about your self-drive trip yesterday?
---Tiring! The road is being widened, and we ____ a rough time.
A．have
B．had
C．would have
D．have had
关于干性坏疽的叙述，下列哪项是正确的
A．发生机制为动脉闭塞而静脉回流受阻B．腐败菌感染一般较重C．全身中毒症状重D．坏死区与周围组织没有界线E．多见于四肢末端
