设a,b为不等的正数,且M=(a4+b4)(a2+b2),N=(a3+b3)2则有( )
A:M=N
B:M<N
C:M>N
D:M≥N
A year has four seasons and it ____________ twelve different star signs.
已知函数f(x)=-2(x+a)lnx+x2-2ax-2a2+a,其中a>0.