Black-box and white-box testing method ale often used in software testing phase, in which, the white-box is mainly used to test software's (73) .

A．external function of a program

B．reasonableness of structure

C．internal logic of a program

D．correctness of a program

汽机单阀切顺阀后，说法正确的是（）。

A、主汽流量、给水流量降低；

B、汽泵转速降低；

C、标准煤耗降低；

D、调门节流损失降低。