Sara and juan conducted an experiment to test which soil would be best for growing plants. they used all three types of soil seen in the jar: sand, silt, and clay. they also made a mixture of soil using equal parts of sand, silt, and clay. the planted bean seeds in four pots and placed the pots in the sunlight. they watered the pots every day and tracked the seed germination and plant growth. which of these is a control of the experiment? a) type of soil b) plant growth c) time needed for germination d) amount of water given to the seeds