We must pay attention to the ____(交通灯).
i, r, p, n, s, g ____
多项式x2+y2、-x2+y2、-x2-y2、x2+(-y2)、8x2-y2、(y-x)3+(x-y)、2x2-12y2中,能在有理数范围内用平方差公式分解的有( )
In summer, most people like to go __________ on vacation.