A central bank is concerned that inflation rates are rising too quickly. In order to reduce the available money supply, it orders banks to set aside a greater percentage of their deposits than previously required. This action best illustrates the central bank's use of which tool of monetary policy?
A. Discount rate
B. Interest on reserves
C. Reserve requirements
D. Open market operations

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.

step-by-step explanation:

idk what the heck he answer is, i’m just putting this here so i finish my account