Cannot alias expression

[John Colvin]

I suspect I'm being very dumb here, but I can't get my head 
around this:

    template B(alias A)
    {
        alias B = A;
    }
    template C(A ...)
    {
        alias C = A[0];
    }
    static assert(B!1 == 1); //fine
    static assert(C!1 == 1); //Error: cannot alias an expression 1