State which correlation coefficient (Pearson, Spearman, point-biserial, or phi) should be used to study each of the following factors:
(a) Activity (active, inactive) and depression (depressed, not depressed)
(b) Time spent at school and time spent studying in hours per week
(c) Veteran (yes, no) and level of patriotism indicated on a rating scale
(d) The hierarchical ranking of a litter of mice for play and social behavior