有关一个概念问题，求解答 additional, schedule, investment, expected, potential

voyage8201

LOS 36.d, 有一句话“Given the expected return (IRRs) on potential projects, we can order the expenditures on additional projects from highest to lowest IRR. This will allow us to construct a downward sloping investment opportunity schedule." 既然给定了IRRs， 怎么还有最高到最低的IRR呢？求大神解答啊。