已知a=log32,那么log38-2log36用a表示是 ( )
A.a-2 B.5a-2 C.3a-(1+a)2 D.3a-a2-1
A
log38-2log36=log323-2(log33+log32)=3log32-2-2log32=log32-2=a-2,故选A.