Select the most appropriate idiom that can substitute the underlined segment in the given sentence.
Even after becoming bankrupt, Charlie is able to maintain an outward show.

The correct option is keep up appearances.

Step-by-step Explanation:

1. Analyze the underlined phrase: The phrase "maintain an outward show" refers to the act of hiding one's difficulties or true financial status, and pretending that everything is still normal, successful, or wealthy to the public.
2. Define the correct idiom: The idiom "keep up appearances" means to maintain an impression of wealth, well-being, or normalcy, especially when faced with adversity, trouble, or financial ruin. This matches the context of Charlie trying to hide his bankruptcy.
3. Analyze the alternative options:
- "Bring down the house" means to perform so well that the audience applauds or cheers enthusiastically.
- "Bell the cat" means to take on a highly risky or dangerous task for the common good.
- "Cut a sorry figure" means to present oneself in a poor, awkward, or unimpressive manner, which is the opposite of maintaining a good outward show.

Therefore, "keep up appearances" is the most appropriate idiomatic substitution.