Answer:
A. Semicolon.
Explanation:
My car is broken therefore, I have to ride the bus this week.
In the above provided sentence, there are two independent clauses joined by the conjunctive adverb 'therefore'. This conjunctive adverb acts as both the conjunction for the two independent clauses as well as an adverb.
Semicolons are used to join sentences, especially independent clauses but in cases like this, there is a conjunction in the sentence.While the use of the comma after 'therefore' is correct, it is also mandatory to use a semicolon after the first independent clause. Also, conjunctions in a sentence should be deleted when used between two independent clauses, but the exception here is that the conjunction used in this sentence is a conjunctive adverb. Instead of removing the conjunction, the semicolon will also be added to the sentence alongside the conjunction.
Thus, the final answer will be
My car is broken; therefore, I have to ride the bus this week.
