Which of the following is an example of nonrandom sampling?
a. using a calculator's random function to generate 12 numbers and using those numbers to choose 12 people from a numbered list.
b. sampling people with the last name anderson by randomly picking a person in the phone book with the surname anderson, then calling every twentieth anderson after that until you've call 15 people.
c. conducting a survey among the teachers at your school by asking your six favorite teachers.