Concept:Darkening the culture bottle blocks light to stop photosynthetic algae from growing in the nutrient solution.
Explanation:The culture solution contains mineral elements used to test plant growth.
When light reaches the bottle, microscopic algae in the solution photosynthesize and reproduce rapidly.
These algae compete with the plant and absorb the mineral elements, which would distort the results.
Darkening the bottle prevents algal growth by removing the light needed for photosynthesis.
This makes the test plant the only organism using the minerals.
Answer:A. prevent algal growth in culture solution