PH3是一种无色剧毒气体，其分子结构和 NH3相似。下列判断错误的是( ) A．
题型：选择题
问题：
PH3是一种无色剧毒气体，其分子结构和 NH3相似。下列判断错误的是( )
A．PH3分子呈三角锥形
B．PH3和NH3分子中孤对电子数相同
C．PH3分子中H原子之间是非极性键
D．PH3分子稳定性低于 NH3分子，因为 N－H 键键能高
题型：选择题
D
College libraries are designed primarily for research and study. To explain its use, let us choose a research topic and follow the step-by-step procedure of looking up the material for the paper. Suppose your assignment is to write a paper on a novel called “The Sun Also Rises” by American writer Hemingway. The first step is to go to the main catalog. Many small drawers on the large wooden cabinets are lined up in alphabetical(字母的) order. Each of the drawers contains hundreds of alphabetical ordered cards. These cards are printed references to all material available in the library. Title cards are cataloged() by the first word of the book title, leaving out the articles like “a”, “an” and “the”. And then you get the cards for the books you need. On the upper left corner of each card is the call number. This is the numerical code that shows where the book is located in the library. The library has open and closed stacks. If your book is on the open stacks, you can go to the open-stack room, and according to the call number find it out by yourself. There are only about 30,000 books on o pen stacks, while most of the 800,000 books in our library are kept in closed stacks, which are accessible only to teachers and graduate students. For undergraduates like you, borrowing books from the closed stacks have to be done with the help of our librarian. In that case, you must fill out a call slip(纸条) for the book, showing the call number, author and title. You can get call slips on tables near the catalog cabinets. You show your call slip together with your library card to a librarian at the information desk. He or she will help you find the book out in the closed stacks.
53.What is the main purpose of this text?
A. To present readers a brief introduction to a college library.
B. To guide readers how to find books needed in a college library.
C. To tell readers how to fill out a call slip in a college library.
D. To show readers where to find books in a college library.
54.What letter you should look for on the title card for the book “The Old Man and the Sea” by the Hemingway?
A. The letter “t”. B. The letter “h”. C. The letter “s”. D. The letter “o”.
55.How are books arranged and shelved in the library?
A. By call numbers. B. By call slips of authors’ names.
C. In alphabetical order. D. By the first word of book title.
56.Suppose you are an undergraduate and you want to borrow a book from the closed stacks, which is the correct order to do it?
a. go to the main catalog b. show your call slip and library card
c. find out the call number d. fill out a call slip
e. get the cards for the books
A.a-b-e-d-c B. a-e-c-d-b C. b-a-c-d-e D. b-c-a-e-d