Final answer:
The most common method of joining copper tube is by soldering with a sweat fitting.
Step-by-step explanation:
The most common method of joining copper tube is by soldering with the use of a sweat fitting. Sweat fittings are made specifically for soldering copper tubes together and they have a smooth end that can be easily inserted into the tube. The solder is then heated to melt and flow into the joint, creating a strong bond.