已知a1，a2，…，an均为正数，且a1•a2…an=1，求证：（2+a1）（2+a2）…（2+an）≥3n．
证明：∵a1＞0，1＞0；2+a1=1+1+a1≥3•
=3•3 1•1•a1
＞0；…（2分）3 a1
同理：2+a2=1+1+a2≥3•
=3•3 1•1•a2
＞0；…2+an=1+1+an≥3•3 a2
=3•3 1•1•an
＞03 an
由不等式性质：上面n大于0的同向不等式相乘，即得：(2+a1)(2+a2)…(2+an)≥3n•
…（4分）3 a1•a2…an
∵已知：a1•a2…an=1，代入上式得：（2+a1）（2+a2）…（2+an）≥3n…（6分）
Big ocean fish have almost been endangered since the start of business fishing in the 1950s. The scientists found that the number of large fish has dropped by 90 percent in the past fifty years. The study took ten years. The researchers collected records from fishing businesses and governments around the world. The magazine Nature published(发表)th  e findings.The scientists say the common way called longline fishing is especially harmful to large fish. This way includes many fishing lines that are connected(连接) to one boat. If these lines are joined together, they can reach one hundred kilometers. They hold thousands of sharp metal hooks(钩) to catch fish. Longline fishing is especially common in the Japanese fishing industry. Records showed that Japanese boats used to catch about ten fish for every one hundred hooks. The study says longline fishing boats now might catch one fish per hundred hooks. The scientists say business fishing can destroy groups of fish much faster than in the past. It’s not the only worry that the number of large fish is becoming smaller and smaller. What’s worse, they are smaller in size than their ancestors(祖先). 根据短文内容完成表格，每空一词。 What is happening to ocean fish?
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