下列收养行为有效的是（）。
A.生父母具有痴呆症
B.生父母送养时隐瞒被收养人失聪
C.福利院将孤儿送养
D.残疾夫妇收养残疾儿童
参考答案：C
After Jack had sent some e-mails, he _______ working on his project. [ ]
A. had started
B. has started
C. started
D. starts
有关孕激素的生理作用正确的是
A．促进乳腺管发育
B．促 * * 上皮角化，糖原增加
C．使子宫肌肉对缩宫素的敏感性增强
D．使宫颈黏液拉丝度加大
E．促使宫颈口闭合
