<span>A.
Half the students were failing the course near the end of the school year.
The sentence is written in passive voice because the course is the subject of the sentence and was being failed is the main verb phrase. The course can't fail. The students are the ones who are failing so to change it you must make the students the subject of the sentence. A is the only option that makes the students the subject.
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Answer:
Third sentence
Explanation:
In the first sentence, therefore is used for reasoning
ex: Therefore, dirty water is bad for the environment because it can make people sick
The second sentence is a run on sentence so it would not be correct.
"During the rock concert" would be the subject, as "an amplifier exploded on stage" would be the predicate.