Which of the Following Function Calls Is a Valid Way

Multiple Choice

Which of the following function calls is a valid way to place elements into vector<char> chars?

A) std::fill(chars.begin() , chars.end() , '5') ;
B) std::fill_n(chars.begin() , chars.end() , '5') ;
C) std::generate(chars.begin() , 10, '5') ;
D) std::generate_n(10, chars.end() , '5') ;