[A] Function
[B] Var
[C] Prototype
[D] Constant

Answer: [B] Function and Var

Explanation: In JavaScript, function and var are reserved keywords. They are pre-defined words that have a special meaning in the language, and they cannot be used as identifiers (variables, functions, classes, etc.) for other programming elements. Reserved words are case-sensitive, so Function and VAR are not valid keywords.