Which of these samples is a valid random sample for the population given? alia questions three students from her class to learn about the movie preferences of students in her school. miles randomly surveys a group of customers at a coffee shop to understand the coffee consumption habits of 18- to 24-year-old americans. carson interviews students working part-time to gather data on the general spending habits of students. lea speaks with the managers at half of the town’s 10 supermarkets, which stock similar items, to find out which breakfast cereal is most popular among the town's residents.

D is the answer to the question.  

To understand these questions, first look at the way the answers are written out.  Alia questions three students from her class, that might be an answer, but she didn't randomly pick them.  Miles randomly surveys a group of customers at a coffee shop, that might be one, but he might have surveyed a 25 year old instead of a 24 year old, so thats not one.  Carson interviews students working part-time to gather data, he didn't select random students, he interviewed all of them, so that is not a valid option.  Lea speaks with the managers at half of the town's 10 supermarkets, which stock similar items, to find out which breakfast cereal is most popular among the town's residents, that one is not stating that she interviewed, but she interviewed half of the 10, which is five, which can be selected randomly.  

So the correct answer is D.