A high school biology class wanted to see how acid rain affects the growth of plants. They purchased 40 of the same exact flowering plant and placed them in the same area, where
they will receive plenty of sunlight. To create the "acid rainwater" the students mixed
vinegar and water until the pH reached 3.0. They watered them daily with acid rainwater
and recorded the observed results daily for 1 week. At the end of the experiment, they
noticed that on day 4, each plant lost about 4 to 5 flowers. The students concluded that
acid rain is harmful to plants. What is wrong with this experiment?
This experiment lacks an experimental group.
This experiment lacks a theory to explain their results.
This experiment lacks variables.
This experiment lacks a control group.