To choose the best option that improves the underlined portion of the sentence, we need to consider clarity and grammatical consistency. The phrase "and it" seems to refer back to a subject but is somewhat vague.
The options are: A. No Change B. It C. He or she D. They
Looking at these options, "They" (option D) is the best choice if the sentence is referring back to a plural subject (like "people" or "individuals"). This maintains consistency in pronouns and improves clarity.
Therefore, the best option is: D. They