Answer:
The answer which shows proper comma usage is the following one:
Mexico is not exempt from earthquakes, nor are they always mild.
Explanation:
Commas are often used to separate different clauses, and that is what happens in the sentence above. Check it out:
Mexico is not exempt from earthquakes, nor are they always mild.
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Clause 1 Clause 2
Both clauses can be called so because both have their own subject and predicate, and both express a complete thought. Therefore, they must be separated by a comma.
