This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to tighten a drive belt
Disconnect the battery.
Before you get started, disconnect the battery to ensure the engine cannot be started while you're working under the hood. As a precaution, always disconnect the battery before putting your hands in the engine bay of your vehicle.

Choices:
(a). Use a hand or socket wrench to loosen the nut holding the ground cable on the negative terminal of the battery, then slide it off the terminal post. You will not need to disconnect the positive cable as well.;
(b). Do not turn the engine off before beginning work. This can cause serious issues with your engine before you know it is covered under your hood.;
(c). If the battery was disconnected before starting the engine, you could get off the hood and disconnect it before beginning the engine. Disconnect the battery from the coil.;
(d). Work through a window up front or from behind the dashboard panel. If you can, use the front left and right hands on the throttle bar, the indicator light, or right door knobs.;
The answer is:
(a).