chronically长期的，慢性的[23] I want to tell you about the past, present and future of the human population, so let’s start with a few problems. Right now, a billion people are chronically hungry. That means they wake up hungry, they are hungry all day and they go to sleep hungry. A billion people are living in slums, not the same billion people, but there is some overlap. Living in slums means they don’t have infrastructure to take the garbage away. They don’t have secure water supplies to drink. Nearly a billion people are illiterate. Try to imagine your life being illiterate. You can’t read the labels on the bottles in the supermarket, if you can get to a supermarket. Two-thirds of those people who are illiterate are women. And about 200 to 250 million women don’t have access to birth control they want, so that they can’t control their own fertility. This is not only a problem in developing countries. [24] About half of all pregnancies globally are unintended. So those are examples of population problems.