单项选择题
A.π<SUB>1</SUB>≠π<SUB>2</SUB> B.π<SUB>1</SUB>=π<SUB>2</SUB> C.μ<SUB>1</SUB>≠μ<SUB>2</SUB> D.μ<SUB>1</SUB>=μ<SUB>2</SUB> E.μ<SUB>d</SUB>=0