下列为性染色体异常遗传病的是 [ ]
A．白化病
B．苯丙酮尿症
C．21三体综合征
D．性腺发育不良症
答案：D
---Did you listen to the lecture given by the famous herbalist doctor Zhang Wuben?
--- No, we ______ it. But we had a lot of traffic on our way.
A．could have attended
B．must have attended
C．could attend
D．shouldn't have attended
课程研制由（）、（）和（）三个阶段构成。
