Can someone plz answer my previous question?

Facial shaving brushes are either bulb-shaped or fan-shaped. an experiment is to be conducted to determine whether the lather thickness is the same for both types of shaving brushes. in previous studies, it was determined that shaving brush size (small, medium, large) is associated with lather thickness, but shaving brush type (wolf whiskers, maggard razors, frank shaving, and so on) is not associated with lather thickness. how could the experiment best be conducted? by blocking on shaving brush size by blocking on shaving brush type by blocking on shaving brush shape by blocking on lather thickness without blocking

Firms use marginal analysis to determine prices by a) changing prices in accordance with information from retailers. b) using comparisons with strong competitors to position prices accordingly. c) examining the effect on revenue of small changes to the price of one item. d) trying to minimize production costs by using better and more efficient methods.

Would enjoy a movie about the subject