Answer:
Use more than one termite and run many trials.
Explanation:
it's not A because we're not trying to figure out pencil's but the chemical's in ink. It's not B because using just one bug wouldn't really get us anywhere. It's not D because you'd actually want to try different brands of ink to see if maybe you had a lesser chemical ratio. It's C because not all the bugs will react in the same way as just one would. Also, doing multiple trials would show us if they would change their behaviors.