吸吮反射消失时间为生后（）
A.2个月
B.3个月
C.4个月
D.5个月
E.6个月
参考答案：C
—I broke the window.
—You ____ play football near the window. [ ]
A should
B. shouldn't
C. had better
D. must
为什么压力容器用钢要严格限制其含碳量
