In a water culture experiment, the culture solution in a transparent beaker turned green. What precaution
should have been taken to prevent the culture solution from turning green?

• A.Changing the culture solution regularly
• B.Increasing the number of times the culture is aerated
• C.Covering the transparent beaker with black cloth
• D.Adding warm alcohol to bleach the green colour
• E.Sterilizing the beaker in a hot oven before use