Rick’s class plans to study the effect of eating different breakfast foods on grades in morning classes. Students in the class will be the test subjects for the investigation. Which of the following would most likely make the results of the experiment invalid?

Question

cuanchi · Answer

show the options

tswift96 · Answer

Half of the students ride the bus to school, and half ride in cars.
Some students eat breakfast two hours before other students do.
Some students miss school during the investigation due to illness.
All students in the investigation have morning classes in the same subjects.

cuanchi · Answer

which one do you think will affect the result?