木桁架的形式有()。
A、长方形
B、折线形
C、拱形
D、梯形
参考答案:B, C, D
以下哪项不是中厚皮片的优点()
A.较柔软
B.能耐受摩擦
C.色素沉着轻
D.可生长在轻微感染经过适当处理的肉芽创面上
E.挛缩较少
______ quite recently, most mothers in Britain did not take paid work outside the home.
A.Before
B.Until
C.From
D.Since