A study was done to find if different tire treads affect the braking distance of a car. What is the independent variable?

a) The tire treads
b) braking the car
c) the type of car
d) none of the above

Plz help me out before in 10min!

No links plz!

What is produced during the krebs cycle? co2, atp, nadh, and fadh2 pyruvate, co2, and atp atp, fadh2, and h2o h2o, adp, and nadh

What came first egg or chicken? and is tomato a vegetable or a fruit?

Residential construction is expanding in florida, the expansion has caused fragmentation of habitats, one of the results of the increased construction is a decrease in the number of large predators such as the coyote, black bear and pool panther, which will be the most immediate local result of this fragmentation? 1)large predators will become extinct 2)decrease in middle sized predators 3)increase in population of top carnivores 4)increase in population of prey species