What is the correct answer ? idk if a is correct

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

What must be true for natural selection to heppen

Cedric has a low fever and minor aches. yesterday, he went to the doctor for his booster shot and receive the flu shot. which best explains why he has this reaction?