Carlo is wondering what causes plants to grow at different rates. carlo’s hypothesis is “plants will grow more when the day is longer.” what would be the difference between the test group and the control group in this experiment?
type of soil
type of plants
exposure to sunlight
method for measuring the growth

The correct answer would be exposure to sunlight.

According to the hypothesis of Carlo, he must study the effect of sunlight exposure on the growth of plants.

For example, in a control group, the plants must get an equal amount of sunlight, say 5 hours daily, as long as the experiment runs.

Whereas in the test group, the amount of sunlight exposure must be different. For example, it might be 3 hours a day in one group while 7 hours a day in another group.

It would help him find the effect of duration of the day or sunlight exposure on the growth of the plants.

b is the best answer for this question.