Q: Pigments in the skin act like a filter that can prevent the skin from making vitamin D. As a result, people with darker skin need more time in the sun than people with lighter skin to make the same amount of vitamin D. Caucasian Americans have lighter skin than other Americans. Researchers were not surprised to discover therefore, that vitamin D insufficiency among Caucasian Americans is more prevalent or less prevalent than among other Americans?
A: less prevalent

Q: The upper rock layers are much younger. Rich was examining a cliff face. Which part of the cliff is younger, geologically speaking the base or the top?
A: the top

Q: The more cylinders a car engine has, the more powerful its engine can be. Chris is going car shopping. He has two choices, a car with 6 cylinders or a car with 4 cylinders. If Chris wants to get the car with the less powerful engine, then he should go with the car with 6 cylinders or 4 cylinders?
A: 4 cylinders

Q: Machines make work easier by increasing the amount of force that is applied, increasing the distance over which the force is applied, or changing the direction in which the force is applied. John observed that machines are not very helpful in performing work because they decrease the amount of force, and also make the distance the force is applied Greater or Lesser?
A: Lesser