Answer :
Answer: Option D
They should determine the average mass of the tomato plants along with the mass of the hornworms
Explanation:
Determining the average mass of the tomato along with the mass of hornworms will tell the researcher whether the hornworms is still feeding on the tomato or not.
If the mass of the tomato is reducing, then the researcher would know that the acid is not effective in keeping the hornworms away from the tomato or otherwise.