What precaution should have been taken to prevent the solution from turning green?

The diagram above is an illustration of the growth of a plant in a water culture. After a few days, the solution turned green and the plant died. Use this to answer this question.

A. use a non-green plant for the experiment
B. aerate the solution daily
C. cover the culture vessel with opaque paper
D. keep cotton wool around the seedling to make it dry

Correct Answer:

Option C – cover the culture vessel with opaque paper