A survey organization draws a sample of 100 households from 10,000 in a certain town, by the following procedure. First, they divide the town into 5 districts, with 2,000 households each. Then they draw 2 districts at random. Within each of the 2 selected districts, they draw 50 households at random. a. This is a probability sample.
b. This is a random sample.
c. There is selection bias.
d. There is non-response bias.