Correct Answer - Option :
strlen:
This is a function defined in the standard C library and doesn’t require any system call to perform its function of calculating the string length.
malloc:
This is a function defined in the standard C library and it does not always invoke the system call. When a process is created, a certain amount of heap memory is already allocated to it, when required to expand or shrink that memory, it internally uses sbrk/brk system call on Unix/Linux
exit:
This is a function defined in standard C library and it always invokes system call every time, flushes the streams, and terminates the caller.
sleep:
This is not even a standard C library function, it is a POSIX standard c library function. Unix and Windows use different header files for it.
Therefore option 3 and 4 are correct options