Select from options: Continue writing the next sentence.

How to use a chemical drain cleaner
Understand what drain cleaners do.
Chemical drain cleaners or openers usually rely on a strong acid or alkali to do the job. These substances both break down and dissolve the clog, and react with the water to form heat.

Possible answers:
(A). Drain cleaners work best on slow moving drains. They are less effective in clogs with standing water.
(B). The acid reaction heats up the drain created by the acid or change the water as a result. When wax or other wet surface has dissolved into the water, the plug changes in the water and any moisture drains out.
(C). Draining, then remove, siphon off the resulting air and the bottled water and discard. The simplest additive for a cheaper drain cleaner is acetone.
(D). Drain cleaners aren't necessary for treating plumbing leaks in apartments or buildings. They're not recommended for residential systems where overheating is a major hazard.
Answer:
(A).