图18-3-31所示电路ab端口电压电流关系式是()。
A.U=2.5-4.5I
B.U=22.5-4.5I
C.U=2.5-7I
D.U=2.5+4.5I
参考答案:A
The answer is connected with the main use ________ the body makes of food to supply the
energy for movement.[ ]
A. where
B. why
C. what
D. that
照片上的光学对比度主要依存于
A.增感屏的感速B.X线对比度C.胶片的反差系数D.显影液的反差度E.胶片感光度