For the following question, refer to the passage titled "The Scientist Experiments" on the Unit Test Reading Passages sheet. Answer the question to improve elements of the passage such as sentence structure, word choice, overall organization, tone, and voice.
Which of the following best replaces the word "it" in Sentence 16?

A. the health of the soil
B. the scientist's interest
C. the question
D. regular watering
E. sunlight