填空题

For Questions 6-10, you will hear a lecture on world population. While you listen, complete the sentences and answer the question. Use not more than 3 words for each answer. You will hear the recording twice. You now have 25 seconds to read the sentences and the question below.
______ people in the world are under the age of 25 or are reaching the childbearing age.

【参考答案】

3 billion