单项选择题
A.n倍 B.n-1倍 C.1/n倍 D.(n+1)/n倍
A.25% B.50% C.75% D.91.74%
A.净功增大,效率提高 B.净功增大,效率降低 C.净功和效率都不变 D.净功增大,效率不变