We are invoking a function called A that takes a single parameter, the data list (B C)

We are invoking a function called A that, in turn, invokes a function called B that takes a parameter C.

We are invoking a function called A that takes two parameters, B and C

This is a single data list that contains three atoms: A, B and C. The parentheses around (B C) are irrelevant in this context, since this is not a function invocation.

This is a data list that contains two elements, an atom and a sublist