最适宜做桥体龈端的材料是()
A．热凝塑料
B．自凝塑料
C．镍铬合金
D．烤瓷材料
E．复合树脂
参考答案：D
Read an judge. (读一读，判断下列句子是“Y”否“N”正确)
( )1. Dongdong is a girl.
( )2. Mr Xue is Mary's teacher.
( )3. Zhang Yuan is Bob's friend.
( )4. Mary is from China.
( )5. Steven is Bob's friend.
平行于面的应力称为切应力，用符号（）表示。
A.σ
B.β
C.γ
D.τ
