题目

在一定条件下，对于密闭容器中进行的反应P（g）+Q（g）=R（g）+S（g）下列说法中可以充分说明这一反应已经达到化学平衡状态的是（  ） A． P、Q、R、S的浓度相等      B．P 、Q、R、S在密闭容器中共存 C．P、Q、R、S的浓度不再变化 D．用P的浓度变化表示的化学速率与用Q的浓度表示的化学反应速率相等阅读理解     Photographs are everywhere. They decorate(装饰) the walls of homes and are used in stores for sales of different goods. The news is filled with pictures of fires, floods, and special events. Photos record the beauties of nature. They can also bring things close that are far away. Through photos,people can see wild animals , cities in foreign lands , and even the stars in outer space. Photos also tell stories.     Reporting the news through photos is called photojoumalism. At times photojournalists tell their stories through a single picture. At other times,they use a group of pictures to tell a story. Each picture is like a chapter in a book,which can do more than record the facts. It can also be a strong force for social change.     Jacob Riis was among the first photojournalists. He took pictures of parts of New York City where the poor lived. Riis believed that poverty (贫穷) caused crime, and he used photos to help him prove hispoint. A few years later,the photos of small children working in factories by Lewis  Hine shocked thepublic. Hine's pictures helped bring about laws to protect such children.     Hundreds of pictures may have to be taken in order to get one or two really good photos. It takes science to have the photo come out clearly and art to make a photo that has a good design and expressesfeeling. Photojournalists make an actual record of what they see. A photo, however,can be both a work of art and an actual record. It can record an important event as a beautiful or exciting picture.     As historical and artistic documents (文献), photos can become more important  over time. Todayphotojoumalists still have their pictures appear in newspapers and magazines. They also publish (发表)them in books and on the Internet.1. The underlined word "They"  in the first paragraph refers to _________.    A. beauties     B. photos     C. goods     D. events2. The photos of the small children by Hine show us that photos _________.    A. are also works of artB. are popular ways of reporting newsC. often shock the publicD. can serve as a force for social change3. What can we learn from the passage?  A. News with pictures is encouraging.B. Photos help people improve their life.C. News photos mean history in a sense.D. People prefer reading news with pictures.4. The text is mainly about _________.   A. telling the story through picturesB. decorating the walls of homesC. publishing historical papersD. expressing feeling through pictures