Final answer:
The best option to vary sentence length in the passage about the Virginia opossum is to combine sentences 5, 6, and 7 into one, using a series to list characteristics of the newborn opossum.
Step-by-step explanation:
The most effective way to vary the length of the sentences in the provided passage is Option 1: Combine sentences 5, 6, and 7 to create a series. This would streamline the description of the newborn opossum, making the information more impactful by listing the attributes in a single, concise sentence.
For example, the revision could be: "It is very small, furless, and sightless." This technique helps to vary sentence length throughout the passage and enhances the flow of the text. On the other hand, the remaining options either do not significantly vary sentence length (Option 3), might make a sentence unwieldy with excessive detail (Option 2), or require altering the intended informational structure of the passage (Option 4).