Multi-select problem: How does the next paragraph end?

How to unblock a drain
Use a chemical drain cleaner.
Using a chemical drain cleaner is one of the most common ways to unclog a drain. Always follow the manufacturer's instructions when using chemical drain cleaners.

Choices:
[A]. Instead of using chemical drain cleaners, you can also purchase chemical drain cleaners at your local hardware store. Begin by filling your drain about halfway with warm water.;
[B]. Plastic or wood drain cleaners can cause thick, stubborn fluid to build up in a drain. If you are unable to resolve the problem yourself, get a professional to.;
[C]. Make sure you buy a drain cleaner that is compatible with your system. If you have a septic tank, you will need to find drain cleaner that is suitable for septic systems.;
[D]. Installation instructions are similar to those of conventional drain cleaners, but differ slightly from that used in traditional plumbing systems. Run water or a hose through the drain at the bottom of the pipe.;
[C].