An introductory phrase or clause is a phrase or clause at the beginning that provides background information. Thus the correct answer is B.
<h3>What is a Clause?</h3>
The smallest grammatical element is a clause. A verb must be present in a clause. A clause usually consists of a subject, a verb phrase, and a predicate. The introductory clause in a sentence will be found at the beginning.
The objective of an introductory clause or phrase is to justify or explain the main sentence. Introduction clauses are dependent clauses that give information about the background.
Therefore, option B is appropriate.
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D the answer is d because it shows the NASA worker needs to make sure they have enough time and etc.
