Aresearcher wanted to know if there is an association between exercise and sleep for the population of 16-year-olds in the united states. she obtained survey responses from a random sample of 2000 united states 16-year-olds and found convincing evidence of a positive association between exercise and sleep. which of the following conclusions is well supported by the data?

a. there is a positive association between exercise and sleep for 16-year-olds in the united states.

b. there is a positive association between exercise and sleep for 16-year-olds in the world.

c. using exercise and sleep as defined by the study, an increase in sleep is caused by an increase of exercise for 16-year-olds in the united states.

d. using exercise and sleep as defined by the study, an increase in sleep is caused by an increase of exercise for 16-year-olds in the world.