Can someone find the independent variable and the dependent variable ?

Independent Variable here is ”Speed”, since the independent variable is defined as (what's the scientist changes or what changes on its own)... And in here, both cars were traveling at 60 mph ’at a certain point, so, one of them might speed up or stay behind/lower it's speed from the other, depending on it's driver’.

Dependent Variable here is ”Distance”, since the dependant variable is defined as (what s being studied/measured).

The correct answer is "hydrogen".