brainliest!!! A student wanted to answer the question, “How does the amount of glycerin affect the size of a bubble blown with soap mixture of water, dish soap and glycerin?”. She decided to test the amount of glycerin added to a soap mixture and used 1 drop, 2, drops, 3 drops, and 4 drops. She would add 10 mL of soap to 50 mL of water for each bubble solution. She measured the size (cm) of the bubble produced for each solution.

What is the independent variable?