钢管桅杆应当有中碳无缝钢管制造。
参考答案：错
It took a great deal of courage to admit that all his efforts had been ____.
A．in vain
B．in turn
C．in return
D．in danger
栓剂中不含有的附加剂是（）
A.抗氧剂
B.防腐剂
C.着色剂
D.乳化剂
E.崩解剂
