导致女方不孕最常见的因素是（）
A.子宫因素
B.子宫颈因素
C.输卵管因素
D.外阴、 * * 因素
E.排卵障碍
参考答案：C
债是按照合同的约定或者依照法律的规定，在特定当事人之间产生的( )。
A．债权
B．债务
C．权利和义务关系
D．财产所有权
基本语法
1. When it gets dark, the people ________ (set) off firecrackers.
2. They ________ (begin) to plant trees as soon as they get to the park.
3. She'll go shopping with me if she ________ (have) free time.
4. If he ________ (come) back,ask him to call me back.
5. He ________ (not come)if you don't invite him.
