You want to test the effect of soil acidity on plant growth. Which of the following is an example of a controlled experiment to test this? O A. The plant type soil acidity amount of light and amount of water are all varied and studied in a laboratory.
O B. The soil acidity of plants in a garden that get light and water from their surroundings is increased after the plants grow to a height of 100 cm.
O C. The plant type amount of light and amount of water are kept constant well so acidity is varied for plants in a greenhouse.
O D. Soil acidity in height of plants growing in 10m^2 yard are measure twice in July and twice in August.