Which of the following function is used to find the first occurrence of a given string in another string?

Answer: Option C

The function strstr() Finds the first occurrence of a substring in another string
Declaration: char *strstr(const char *s1, const char *s2);

Return Value:
On success, strstr returns a pointer to the element in s1 where s2 begins (points to s2 in s1).
On error (if s2 does not occur in s1), strstr returns null.