(-x+y)( )=x2-y2,其中括号内的是( )
A:-x-y
B:-x+y
C:x-y
D:x+y
下列各组数中,能构成直角三角形的是( )
Cu、Cu+、Cu2+三种粒子,都有相同的 ( )
____ he ____ help his mother ____ housework?