RS-232C关于机械特性的要求，规定使用一个 【4】 根插针的标准连接器。
参考答案：Y
水塔地面标高20m，塔底高15.5m，控制点5000m远，该点地面标高为12m，已知i=0.15%，则根据最小服务水头该点最多为______层。
A．1 B．2 C．3 D．4
Accoding to the old stories of Iceland and Norway,Eric the Red was forced to leave Iceland because he had committed a murder,_______he got into trouble.
A.for which B,at which C.in which D.with which
