机组突发人身事故或设备故障时应立即按动（）。A.停机按钮 B.紧急停机按钮 C.主电

It was not until dark _____ he found _____ he thought was the correct way to solve the problem．

A．when; that

B．that; that

C．when; what

D．that; what

Thanks for             me with my math. [ ]

A. help

B. helps

C. helping

D. helped

何谓软件维护的成本？如何度量软件维护的工作量？

砖柱排砖时应使砖柱上下皮砖的竖缝相互错开1/2砖或1/4砖长。