A music teacher wants to determine the percentage of students at her school that read music. Without warning, she conducts a sample survey of the students in her introductory music class. Which option below best describes the sample she collects?
A. The sample is random because she chose the class to survey at random.
B. The sample is random because she did not warn the students in the class.
C. The sample is biased because the students are in music class.
D. The sample is biased because she did not warn the students in the class.