短信预约提醒成功
There was a serious accident in the chemistry lab last week，A confused student accidentally poured a wrong mixture of chemi-cals in test tube.There was a strong explosion.Broken pieces ofglass from the test flew in al!directions.A sliver of flying glassfound its mark in John Martin's right arm.The lab instructor sawblood trickling from John's arm.He immediately notified theuniversity's infirmary about the accident。
We can see from the chart that the world population is increasing rapidly.By the year 2000，the world population will have dou-bled from that in 1960.1960 saw the world with only about 3 billion people，but by the year 2000，the number will shot up to more than 7 bil!ion 400 million.