脆化
参考答案：
脆化是指材料韧性急剧下降，而由韧性转变为脆性的现象。
膀胱过度活动症的核心症状是（）.
A.尿频
B.夜尿
C.尿失禁
D.尿急
E.尿痛
33．_______the activities might seem childish, in reality they require a lot of strength and determination.
A．When
B．As
C．While
D．Once
