Identify the sampling method used in each situation:

a. At a large university, all instructors in 3 office buildings are interviewed to determine their level of research interest.

b. A manufacturer checks every 20^thproduct on its assembly line for quality assurance.

c.6lottery balls are drawn from a hopper of 269 equal size balls.

d.Everyone who walks into the grocery store between 3:00pm and 5:00 are asked their opinion about a new traffic light being installed next door.