I think the answer would be answer choice B
It might help if we could see what the paragraph and choices were :)
Options C and D feature parallel structure.
Parallel structure occurs when the same grammatical pattern is used. In options C and D, the same grammatical pattern is used in each: both are questions, and both begin with a verb followed by the subject.
Answer:
c. because the text follows the history of smallpox from its beginning to its eradication, or end
Explanation:
The text is organized in chronological order, going from when smallpox first started to when vaccination replaced variolation. The beginning helps provide evidence and support for how Jenner helped to spread immunization.
