Alittle would be !

braxton is testing 2 different types of motor oil in his truck to determine which one lasts longer between oil changes. he purchases brand a and brand b from the auto parts store. he adds brand a to his truck and brand b to his sister's car. he then compares the color of the oil at the end of the week from both vehicles and determines that brand b goes longer between oil changes because it is lighter in color than that of brand a when he examines it. why is braxton's conclusion not valid?

a. he added brand b to his sister's car, not the truck.
b. he did not determine the starting color of the oil.
c. he purchased 2 different types of oil.
d. he added brand a to his sister's car, not the truck.