Answer:
Choice C is the correct answer.<em> </em>
Explanation:
The question speaks to the subject of Essential and Non-essential clauses.
Recall that an <u>adjective clause </u>is a dependent clause that acts like an adjective in the sentence. Why? because it gives more information about a noun or pronoun in the sentence. It is dependent because by itself, it makes no sense.
Sometimes the information given by the adjective clause is <u>essential</u>. An essential adjective clause is one that is needed for the sentence to make sense. If you took it out, you would not know all the information that you need to know.
At other times, such as in the question, the information given by the adjective clause is <u>nonessential</u>. A nonessential adjective clause is one that is not required to enable the comprehension of the sentence. In other words, the sentence still makes sense and you know everything you need to know even without the clause. So, you could take it out.
When a sentence has a nonessential adjective clause, the clause is set apart with commas. This shows that it is not essential.
Given the above, it is clear to see that from the sentence, 'which is not his first career' qualifies the opening clause 'A career in politics' but is not required to comprehend the whole sentence if removed.
E.g A career in politics ended up being the ticket to success for Abraham Lincoln.
So to correctly punctuate using a comma, we could separate the nonessential information as follows:
A career in politics, <em>which was not his first career,</em> ended up being the ticket to success for Abraham.
Cheers!