What is the purpose of the given C code?

#include <stdlib.h> 
_Mbsave _Mbxtowc = {0};  
int (mbtowc) (wchar_t *pwc, const char *a, size_t n) 
{
return (-Mbtowc (pwc, s, n, &-Mbxtowc) ) ;
}

A. strlen() B. strlength() C. stringlen() D. strsize()

A. To print formatted text to the standard output B. To read text from the standard input C. To open a file D. To close a file

A. math.h B. stdlib.h C. cmath.h D. algorithm.h

A. Compares two strings and returns an integer indicating their relationship B. Copies one string to another C. Concatenates two strings D. Searches for a substring