单项选择题
A.15 B.16 C.31 D.32
A.1 2 3 4 ((M*M)*M)*M B.1 2 3 4 (M*M)*(M *M ) C.1 2 3 4 (M*(M *M))*M D.1 2 3 4 M*(M *(M *M ))
A.10 B.9 C.8 D.7