I wanted to test different amounts of fertilizer to see which was best for growing grass. I mixed water with different amounts of fertilizer, and then added sodium polyacrylate to change it into a gel. Then I sprinkled the grass seeds on top, and waited for them to grow.

I really need a control group for this experiment. What would I use for a control?

1. Water, fertilizer, and grass seed, without any sodium polyacrylate.

   No. For the control, we want to skip the thing we are testing for. We are not testing changes caused by the amount of sodium polyacrylate.

2. Water, sodium polyacrylate, and grass seed, without any fertilizer.

   Yes! We are testing to see how different amounts of fertilizer change the growth of the grass. The amount of fertilizer is the variable we are testing, so the control group should not have any fertilizer.

3. Water, sodium polyacrylate, and fertilizer, without any grass seed.

   No. For the control, we want to skip the thing we are testing for. We are not testing changes caused by the amount of grass seed, and we know that no grass will grow if we do not have any seeds.

4. Sodium polyacrylate, fertilizer, and grass seed, without any water.

   No. For the control, we want to skip the thing we are testing for. We are not testing changes caused by the amount of water.

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