With more forests being destroyed, huge quantities of good earth _____ each year.
A:is washing away
B:is being washed away
C:are washing away
D:are being washed away
已知x=1是一元二次方程x2-mx+n=0的一个根,则m2-2mn+n2的值为____ .
已知△ABC中,AB=AC,则cosB+cosA的最大值为____