螺旋楼梯所特有的部件是（）
A.支撑梁
B.侧弦
C.梯级
D.中柱
参考答案：D
ERP集成了企业（）三大资源。
A.资金流
B.物流
C.信息流
D.程序流
—Why did you cancel your trip to the New York?
—We were just about to leave_______ it started to snow．
A．when
B．before
C．after
D．since
