操作时，应先慢慢起升，待链条张紧后，检查葫芦各部分有无异常，挂钩是否妥当。当确认各部分安全可靠后，才能继续起吊。
参考答案：对
Be quiet, please. The students _______ a class now. [ ]
A. have
B. had
C. are having
D. were having
HIV主要感染（）
A.神经胶质细胞
B.CD4T淋巴细胞
C.单核细胞
D.B淋巴细胞
E.皮肤上皮细胞
