A researcher wants to determine if lead levels are different between the top of a glass of water and the bottom of a glass of water. Many samples of water are taken. From half, the lead level at the top is measured and from half, the lead level at the bottom is measured. Would this be a valid matched pair test?

a. No, as the lead levels cannot be accurately measured

b. No, as the measurements of top and bottom should be from the same glass

c. Yes, as long as there are an equal number of glasses in each group

d. Yes, as long as they are all from the same faucet