Which of the following is used on Solaris?

Answer: Option C

This question asks about the software used on the Solaris operating system. Let's break down the options:
Option A: gcc - gcc is a very popular compiler used on various systems, including Linux, but it's not specifically tied to Solaris.
Option B: clang - Clang is another compiler, also used on many platforms, but not specifically designed for Solaris.
Option C: Sun Studio - This is the correct answer! Sun Studio is a suite of software tools developed by Oracle (formerly Sun Microsystems) specifically for developing applications on the Solaris operating system.
Option D: FreeBSD - FreeBSD is a Unix-like operating system, completely different from Solaris.
So, the answer is Option C: Sun Studio.