80%的小儿动脉导管解剖闭合的年龄是（）
A.4个月内
B.6个月内
C.8个月内
D.12个月内
E.18个月内
参考答案：A
The audience ______ when they heard the humorous story.
A．burst into laughing
B．burst out laughter
C．burst into laughter
D．burst in laughing
