The Code Segment from Build_reverse, a Member Function of Palindrome_Finder

Multiple Choice

The code segment from build_reverse, a member function of Palindrome_Finder, has been incorrectly altered.
The line __________ replaces the error written into the code segment.

A) while (char_stack.empty() )
B) result = char_stack.front() ;
C) result += char_stack.top() ;
D) char_stack.push() ;