National Center for Construction Education & Research (NCCER) Plumbing Level 1 Practice Exam

Using elbows is the most appropriate choice for connecting two pieces of copper tubing at an angle. Elbow fittings are specifically designed to change the direction of the pipe run, allowing for the creation of bends at various angles, commonly 45 degrees or 90 degrees. This is essential in plumbing where space constraints or the layout of the piping system requires directional changes.

Straight couplings, on the other hand, are intended for making straight connections between two pieces of pipe without altering the direction. They do not serve the purpose of connecting at angles. Tees are fittings that create a junction from one pipe to two others, often forming branches, but they do not facilitate angled connections between two pieces of tubing. Caps are used to close the ends of pipes and do not connect two pipes at angles either. Thus, elbows are the optimal choice for forming angled connections in plumbing systems.