当重物快速下降或用快放落钩而中途急停时，会使起重机失稳。
参考答案：对
—How did your students express their thanks to you on Teachers’ Day?
—A gift together with many flowers _______ sent to me .
A．was
B．am
C．have been
D．had been
下列内容不属于期间费用的是()。
A.管理费用
B.制造费用
C.销售费用
D.财务费用
