In many countries it has been observed that, when high marginal rates of income tax imposed on richer groups are reduced, the tax revenue raised increases. What is an implication of this observation? A Government policy should aim to minimise the income tax. B Sales taxes are always superior to income taxes as a means of raising revenue for the government. C Tax policy intended to reduce income tax on the rich may make the poor better off. D The government should always levy proportional rather than progressive income taxes.