Statistics and Probability A mobile phone company are interested in the number of text messages sent by their customers on a weekly basis. 100 customers were randomly sampled from the company's customer database and asked how many text messages they had sent in the previous week. The average number of text messages was 20 messages/week. What is the sample:

A. The number of text messages sent in the last week. B. The sample average number of text messages at 20 messages/week. C. All customers of the mobile phone company. D. 100 customers included in the study. E. Company's customer database.