A student is investigating gas production of water plants of various sizes. She predicts that larger plants produce more oxygen. She places a test tube and funnel upside down over a water plant submerged in water. The test tube collects gas the plant produces when in sunlight. A diagram of her setup is shown below.
In this experiment, what is the independent variable?
A.The number of gas bubbles
B. The varying size of the plants
C. The test tube used to collect gas
D. The temperature of water in the beaker
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