—Oh, really? Have you got any valuable idea?
A:which
B:who
C:what
D:why
用NA表示阿伏加德罗常数的值,下列物质中物质的量最大的是( )
①∀a,b∈N*,a≠b有af(a)+bf(b)>af(b)+bf(a);
②∀n∈N*,有f(f(n))=3n,
则f(1)+f(6)+f(28)=____.