下列不是工程中常见约束的是（）
A.柔体约束
B.铰链约束
C.摩擦约束
D.链杆约束
参考答案：C
— The students sitting at the back can't see the blackboard ______.
— Why not ______ them move a little forward? [ ]
A. clear enough, let
B. enough clear, letting
C. clearly enough, let
D. enough clearly, letting
What honest boy! And he is best student of all.
A．a; a
B．an; /
C．a; the
D．an, the
