Econ MC問題,[HELP]

1.) A piece of land is used for the construction of a cultural centre but not a residential building.
The construction of a cultural centre and the construction of a residential building will have different returns and thus will involve different opportunity costs.

2.) A pile of paper is used to print textbooks but not reference books.
The production of paper to print text books and the production of paper to print reference books will have different returns and thus will involve different opportunity costs.

3.) A doctor is thinking of switching to another occupation.
To continue the occupation as a doctor and to switch to another occupation will have different occupation will have different returns and thus will involve different opportunity costs.
Given all the three decisions will involve different opportunity costs, thus only
Answer (D) is correct.
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D. (1), (2) and (3)