Give an example of three variables for which the effect of x1 on y would be

(a) Spurious, disappearing when x2 is controlled.

(b) Part of a chain relationship, disappearing when a mediator variable x2 is controlled.

(c) Weakened, but not eliminated, when x2 is controlled.

(d) Unaffected by controlling x2.

(e) Different at different levels of x2 (i.e., showing interaction).

(f) Confounded with the effect of x2.