（）is a method of constructing a project schedule network diagram that uses boxes or rectangles, referred to as nodes, to represent activities and connects them with arrows that show the dependencies.

This method includes following types of dependencies or precedence relationships:（）, the initiation of the successor activity, depends upon the completion of the predecessor activity.

（）, the initiation of the successor activity, depends upon the initiation of the predecessor activity.

（）, the initiation of the successor activity, depends upon the initiation of the predecessor activity.

A．F-S

B．F-F

C．S-F

D．S-S

冷热交换管路检查时如有漏水现象应该（）。

A.拧紧或更换接头

B.清洗接头

C.卸下接头

D.清洗管路