The best choice to complete the text is Option D: meteoroids, their. This option correctly uses a comma to connect 'meteoroids' with 'their velocity'. It maintains clarity and fluidity in the sentence structure.
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The correct choice to complete the sentence based on the conventions of Standard English is A. meteoroids; their .
Here's why:
Semicolon Usage : A semicolon is used to connect two closely related independent clauses. In this case, 'meteoroids' ends the first independent clause, and 'their velocity upon entering Earth's mesosphere...' begins the second independent clause. The semicolon neatly separates these related thoughts and emphasizes their connection.
Independent Clauses : Both parts of the sentence on either side of the semicolon are independent clauses. This means they can stand alone as complete sentences, which is why a semicolon is appropriate.
Completing the Sentence : By using a semicolon followed by the pronoun 'their', the sentence correctly and clearly conveys its meaning. It shows that the velocity referenced belongs to the meteoroids that we discussed earlier in the sentence.
Therefore, with the choice A. meteoroids; their , the sentence reads smoothly and logically, adhering to the proper grammatical structure.