Probably because of history relation.
YES YES YES YES YES YES YES YES I don’t get what u are saying but points for me!
A dependent variable is how they are recording, measuring or keeping track of the science experiment their doing.
A independent variable is the things/types there using to compare what is the most/least affective in the experiment.
A controlled variable is something that stays the same in the experiment or a group/set used for comparison
The numbers are 2 of them