The New York City school district is planning a survey of 1,000 of its 250,000 parents or guardians who have students currently enrolled. They want to assess the parents' opinion about mandatory drug testing of all students participating in any extracurricular activities, not just sports. An alphabetical listing of all parents or guardians is available for selecting the sample. In each of the following descriptions of the method of selecting the 1,000 participants in the survey, identify the type of sampling method used (simple random sampling, stratified sampling, or cluster sampling).

a. Each name is randomly assigned a number. The names with numbers 1 through 1,000 are selected for the survey

b. The schools are divided into five groups according to grade level taught at the school: K-2, 3-5, 6 -7, 8-9, 10 -12. Five separate sampling frames are constructed, one for each group.Asimple random sample of 200 parents or guardians is selected from each group.

c. The school district is also concerned that the parent or guardian's opinion may differ depending on the age and sex of the student. Each name is randomly assigned a number. The names with numbers 1 through 1,000 are selected for the survey. The parent is asked to fill out a separate survey for each of their currently enrolled children.