Explain clearly.

For questions 1 -3: Suppose there are two types of persons: high-ability and low-ability. A 2-year master degree costs a high-ability person $X and costs a low-ability person $30,000. Firms intend to pay $40,000 to workers without a master degree and $60,000 to those with one. + 1. For high-ability person, the marginal rate of return is . And it's for low-ability person. A. 50%; 50% B. 50%; 25% C. 25%; 25% D. 25%; 50% 2. In what range must X be such that firms can use education as a screening device? A. "X>$20,000 B. X$30,000 3. Assume ability difference is fully represented by the difference in discount rate, the discount rate of the high- ability is A. >25% B. $25% C. >50%