Which of the following are random samples from the specified populations and which are not? Why?

(a) An experimenter selects every 10th name in the telephone book for her city, starting with one name that is chosen blindly. Population: all those with listed telephone numbers in her city.

(b) Teenage American students taking introductory psychology at University X volunteer to participate in an experiment. Population: all American teenagers.

(c) The names of all students at one particular college in the United States are written on slips of paper and placed in an extremely large hat. The slips are well shuffled, and 50 names are drawn blindly to serve as participants in an experiment. Population: all students at this college.

(d) The procedure is the same as in part (c) but the population is all college students in the United States.