Software design is a (66) process. It requires a certain (67) of flair on the part of the designer. Design can net be learned from a book. It must be practiced and learnt by experience and study of existing systems. A well (68) software system is straight forward to implement and maintain, easily (69) and reliable. Badly (68) software systems, although they may work are (70) to be expensive to maintain, difficult to test and unreliable.

67（）

A．amount

B．amounted

C．mount

D．mounted

抽油机井管柱在抽油泵下部连接筛管和（），起到一定的防砂和沉砂作用。

A、防砂管

B、尾管

C、丝堵

D、泄油器