From four agricultural plots, two will be selected at random for a pesticide treatment. The other two plots will serve as controls. For each plot, denote by S the event that it is treated with the pesticide. Consider the assignment of treatment or control to a single plot as a trial.

(a) Is P(S) the same for all trials? If so, what is the numerical value of P(S)?

(b) Are the trials independent? Why or why not?