For the following studies in which tests comparing two means are conducted, select whether the populations are independent or matched pairs:

a. A study is conducted to see what effect a new drug has on dexterity. A random sample of 30 people is chosen. They are given a series of tasks to perform and a score reflecting their performance. A dose of the drug is administered to the 30 people, and they are then given a similar series of tasks to perform and scored again.
b. A study is conducted to determine the difference between the average amount that people spend on durables and non-durables when they go shopping. A sample of people is chosen and their shopping purchases are observed.
c. A study is conducted to determine if there is a difference between the average length of time spent in traffic on the way to work and the average length of time spent in traffic going home from work for people in a city. A random sample of workers is chosen and asked how long they spend getting to work. Another separate random sample of workers is chosen and asked how long they spend getting home from work.