Question

what is the meaning of get to the bottom of something?
cindy got to the bottom of the problem when she finally found out that the heat got turned off because the bill had not been paid.
to take a big risk
to find the real cause of something
to climb down into something
submit
work it out

Explanation:

In the example sentence, Cindy found the real reason (the bill not being paid) for the problem (heat being turned off). "Get to the bottom of something" means to discover the real cause. "To take a big risk" is about risking something, and "to climb down into something" is a literal climbing action which doesn't fit the context.

Answer:

to find the real cause of something