下列多项式能用平方差公式分解的因式有( )
(1)a +b (2)x -y (3)-m +n (4)-ab (5)-a +4
A:2个
B:3个
C:4个
D:5个
下列变化中,属于化学变化的是( )
识别下列各图,回答相关问题:
My grandfather is fond of talking about the good old days, ___ is often the case with old people.