Final answer:
A tubing or flare nut wrench is correctly referred to as a line (option D) wrench. It is designed to fit snugly over a flare nut commonly used on brake or fuel lines, preventing slippage and damage to the fitting.
Step-by-step explanation:
A tubing or flare nut wrench is also known as a line wrench. This tool is specifically designed for use on fittings that employ a flared end fitting for sealing, such as those found in brake or fuel lines. Unlike regular wrenches, a line wrench has an opening that looks somewhat like a boxed end, but with a small slit to slide over the line and onto the fitting. Thus, the correct answer is D) Line.
Line wrenches are particularly useful as they provide a snug fit and avoid slipping and rounding off the corners of the flare nut, which is common with standard wrenches, especially in tight spaces where the fittings are hard to reach or where they cannot be approached straight on.