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 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 B. Soil acidity and height of plants growing in a 10 m2 yard are
measured twice in July and twice in August.
c. The plant type, amount of light, and amount of water are kept
constant while soil acidity is varied for plants in a greenhouse.
OD. The plant type, soil acidity, amount of light, and amount of wnter
are all varied and studied in a laboratory.