Final answer:
The idiom that represents the idea of people getting excited about something that might happen but hasn't happened yet is 'Don't count your chickens before they hatch.'
Step-by-step explanation:
The idiom that represents the idea of people getting excited about something that might happen but hasn't happened yet is B. Don't count your chickens before they hatch.
This idiom means that you should not assume that something will happen before it actually happens. Just like how you shouldn't count the chickens you expect to hatch from eggs before they actually hatch.
For example, if someone says they are going to win the lottery, you might say, 'Don't count your chickens before they hatch!' because there's no guarantee they will actually win.
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