—Are you ____________?
—No. I am ____________ doing my homework.
A:free, free
B:free, busy
C:busy, free
D:busy, busy
用配方法将二次三项式a2-4a+5变形,结果为( )
下列关于植被类型的叙述,错误的是( )
下列说法正确的是( )