Answer:
C). Added introductory words or phrases.
Step-by-step explanation:
Introductory words or phrases are described as the adverbs or interjections that are primarily employed to introduce a sentence in order to establish connectivity between the ideas and ensure a smooth transition.
In the given sentence, 'introductory words or phrases' have been added to revise the sentence. The introductory word 'because' functions to link the two ideas(I studied hard and I did well on the exam') together in a cause-and-effect structure. It converts the first clause('I studied hard') into a 'dependent clause'('Because I studied hard') that is setting the stage for main clause to ensure a smooth transition between ideas and enhance its efficacy. Therefore, option C is the correct answer.