Coins
Coins were first invented in the 7th century B.C.. in Lydia. They were made from gold and silver. People made coins of different sizes and gave them different values. Coins were good in many ways. First, they could be carried easily. Second, they made exact exchanges possible. Everyone like the idea, so quickly became popular.
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Q: What does 'the idea' refer to in the last sentence?
The idea means the use of coins.
In the last sentence, "the idea" refers to the concept of using coins as a form of currency. This refers to the idea that coins, with their standardized sizes and values, could be easily carried and used for exact exchanges.
To find the answer, you can identify the context of the sentence and understand the meaning of the phrase as it is used in that context. In this case, the previous sentence mentions the positive aspects of coins, such as their ease of carrying and ability to facilitate exact exchanges. Therefore, it can be understood that "the idea" is referring to the concept or notion of using coins for these purposes.