光学对比度与照片清晰度的关系是（）
A.D=lgI0/I
B.K=D1-D2
C.K=rlgKx
D.S=H/K
E.R=1/2d
参考答案：D
– I joined the League ________ May, 2009. What about you?
– I’ve been a League member _______ three years.
A．in; for
B．on; in
C．on; for
D．in; since
他小时候不是很胖。
