Use reasoning to lead to the answer of the following question:
The mailbox is just inside the entrance of what structure containing many homes?\nOptions:\n- beehive\n- porch\n- post office\n- apartment building\n- front door
 Reasoning process:
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An apartment has many homes. There are mailbox at entrance of an apartment building to store all mails for all homes. Therefore, the final answer is apartment building.
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