How is the phosphorus cycle different from the oxygen, nitrogen, and carbon cycles

Which of these serves as a reference for comparison during a scientific investigation? a)outcome variable (dependent variable) b) test variable (independent variable) c)control group d)hypothesis

Ialready know the answers to these questions and they are on the attachment. but i just need to know why that answer is the correct one. plz asap! this is for a report that i need to email by 10!

If a strand of dna has 35% thymine. what is the percentage of cytosine, adenine, guanine?