Concept:The acceleration principle describes the relationship between income and investment in income determination theory. It shows that a change in income triggers a change in investment.Explanation:The acceleration principle emphasises that income or national output is the cause, while investment is the effect. When national income rises, consumer demand increases, and firms respond by investing in more capital goods to expand production. This investment response is often quicker and larger than the original change in income, which is why it is called the acceleration principle. It is the opposite of the multiplier principle, where investment acts as the cause and income becomes the effect. Since income drives investment, the correct option must state that income has an effect on investment.Answer:Option C — income has an effect on investment.