What is linux? what is it good for. And why do people use it?

Linux is Unix-based and Unix was originally designed to provide an environment that's powerful, stable and reliable yet easy to use. Linux systems are widely known for their stability and reliability, many Linux servers on the Internet have been running for years without failure or even being restarted

Explanation:

Linux is used for commercial networking

answer; i believe the correct answer is (b) by using a multimeter;