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A.a+b B.-a+(-b)
C.a-b D.b-a
△ABC中,=a, =b,则等于( )
A．a+b B． —(a+b) C．a-b D．b-a
=a,
=b,则
等于( ) 
="a," 
=b,则
等于( )
=a, 
=b,则
等于( )
=a, 
=b,则
等于( )