当遇到老师的不公平对待时，作为学生，应该（    ）

①有意疏远老师，避免再次发生误会     ②选择恰当的机会，主动解释清楚

③铭记在心，借机批驳老师                  ④学会从老师的角度想一想

根据短文内容，选择正确答案。

Today there are policemen everywhere, but in 1700, London had no policemen at all. A few old men used to protect the city streets at night and they were not paid.

About 300 years ago, London was starting to get bigger and more and more people began to live there. The city was very dirty and many people were poor. There were so many thieves who stole money in the streets that people stayed in their homes as much as possible.

    In 1750, Henry Fielding started to pay a group of people to stop thieves. They were like policemen and were called “Bow Street Runners” because they worked near Bow Street.

    Fifty years later, there were 120“Bow Street Runners”, but London had become very big and needed more policemen. So in 1829, the first Metropolitan(or London) Police Force was started with 3, 000 officers. Most of the men worked on foot, but a few rode horses. Until 1920 all the police in London were men.

     Today, London police are quite well paid and for the few police officers who still ride horses, the pay is even better than for the others.

CH₄和某种氮氧化物反应的化学方程式为CH₄+2口N₂+CO₂+2H₂O，则框内物质的化学式是（　　）

____是构成生物体的基本单位。