conclusion hypothesis control group experimental group
I gave my students this multiple choice question: Lea is investigating how phosphates affect oxygen levels in pond water. For part of the investigation, she uses pond water that contains no phosphates. The pond water without phosphates would be what part of the investigation?

Only one answer is correct among these 4 choices:
- conclusion
- hypothesis
- control group
- experimental group

Could you tell me which one is correct?

control group