Which of the following statements are true about the use of different discount rates for different types of projects?

I. Low-risk, short-term projects may be evaluated by using a short-term opportunity cost.

II. High-risk projects may be evaluated by using a discount rate that is greater than the company's normal opportunity cost.

III. A short-term investment (or borrowing) rate may be used as the company's short-term discount rate.

IV. The use of a lower discount rate for riskier projects forces riskier projects to earn higher rates of return.