In spanish, por and para
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a. each used for specific purposes for different situations.
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b. used interchangeably.
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c. always used together in the same utterance
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d. never used together in the same utterance.

A.) each used for specific purposes for different situations.

Explanation:

"Por" is used to explain the cause, reason or motive of something; while "para" is used to refer to the purpose of an action.

We do things "por" a cause "para" achieve a purpose.

We do things "for" a cause "to" achieve a purpose.