Which one of the following expressions best states the idea of opportunity cost?

A) "A penny saved is a penny earned."
B) "He who hesitates is lost."
C) "There is no such thing as a free lunch."
D) "All that glitters is not gold."

Opportunity Cost

The cost of an alternative that must be forgone as a result of choosing another option, representing the benefits that could have been received by taking a different path.

Free Lunch

An expression indicating that obtaining goods or services without cost or effort is impossible in economic terms, as there's always a trade-off.