Answer:
The correct answer will be option-B.
Step-by-step explanation:
The student performed the experiment to study the effect of talking to plants on the growth of plants. He wanted to study "talking as an experimental variable".
While experiment he divided the samples into control group as well as the experimental group but he mixed the other variables like watering the plants using various methods-directly or with sprinkles in different amount.
This mixing of variables will cause interference with the conclusion as one will not be able to suggest that the growth pattern in plants is the result of the talking or watering. Also, the amount of water as well as mode of providing water differed in the experimental group.
Thus, Option-B is the correct answer.