exercises

阅读下列短文，根据短文内容从每题所给的A、B、C、D四个选项中选出最佳答案。（每小题2分）
It’s said that a thousand years ago there were less than 400 million people on earth. Today, however, the world’s population has come  to 5,000 million. What is worse, it keeps growing at a surprising speed. If this continues, the world’s population will shoot up to 8,000 million by the year 2025. This is what we call population explosion（人口爆炸）.