A:None
B:Either
C:Any
D:Neither
抛物线y2=4x的焦点坐标是( )
已知实数m,n满足:关于x的不等式|x2+mx+n|≤|3x2﹣6x﹣9|的解集为R
(1)求m,n的值;
(2)若a,b,c∈R+,且a+b+c=m﹣n,求证:a+b+c≤3