流产最常见的原因是
A．胚胎染色体结构或数目异常
B．黄体功能不良
C．细菌及病毒感染
D．母体有全身慢性疾病
E．子宫畸形或发育不良
参考答案：A
______ the afternoon of November 1st, they are visiting their teacher. [ ]
A. At
B. In
C. On
D. Of
