B the rate remains the same even if income increases or decreases
The government or tax collecting authority sets a fixed percentage of income, and then requires that percentage of every dollar paid as tax. This is in comparison to a progressive marginal tax rate which taxes at a fixed amount different brackets of income, but higher brackets are taxed at a higher rate. Proportional remains the same amount out of every dollar earned up to an unlimited amount or down to an income of $0.
