ANSWER : C

Explanation :

Keywords in 'C' :

int, char, float, long, double, short, signed, unsigned, near, far, huge, if, else, for, while, do, break, continue, switch, case, default, goto, return, void, enum, struct, union, auto, register, static, extern, typedef.

A keyword cannot be used as a variable name. "real" is not a keyword, hence it can be used as a variable name.