A:ax﹣bx和ay﹣by
B:2a﹣3b和4a2﹣6ab
C:(a﹣b)2和(b﹣a)2
D:xy+xz和xy﹣z
Zhao Pei has to learn ____ (play) the piano on weekends.
既在陇海线,又在京沪线的铁路枢纽是( )
这个周末我们为何不去游泳呢?
____ ____ ____go swimming this weekend?