单项选择题
A.ab=cd B.ac=bd C.a+b=C+d D.bc=ad E.以上结果均不正确
A.22n+2+1 B.22n+2-1 C.22n+1-1 D.22n+1+1 E.以上结果均不正确
A.17 B.18 C.16 D.15