Tell whether each of the following is simple random sampling, stratified sampling, cluster sampling, or systematic sampling.

(a) A teacher puts students' names in a hat and chooses without looking to get a sample of 3 students.

(b) There are 6 models of a car. A truck manufacturer selects 3 trucks at random to sample from each of the models.

(c) Security workers at an airport randomly choose one of the first 50 people to pass through a checkpoint for extra security screening. After that person, they choose every 50th person who passes through for extra screening as well.