Which of the following options would be considered independent samples? a. A group of teenagers (age 13-19) measured on preference for Yellowstone National Park before and after visiting.
b. A group of teenagers (age 13-19) and a group of adults (age 20 or older) measured on preference for Yellowstone National Park before and after visiting.
c. A group of teenagers (age 13-19) measured on preference and brand attitude for Yellowstone National Park before and after visiting.
d. A group (age 13 and older) measured on preference for Yellowstone National Park before and after visiting.