题目内容：

One day, a professor entered the classroom and asked his students to prepare for a surprise test. They waited anxiously at their desks for the test to begin. The professor______ the question papers，with the text facing down as usual. ______ he handed them all out, he asked his students to _______ the page and  begin. To everyone’s surprise, there were no ______, just a black dot in the center of the page.

The professor, seeing the expression on everyone’s face, told them the following：

“I want you to write what you ______ there.”

The students, ______, got started on the inexplicable (费解的) task.

At the end of the class, the professor ______ all the answer papers and started reading each one of them aloud in front of all the students. All of them, with no ______, described the black dot, trying to explain its position in the middle of the sheet, etc. After all had been ______, the classroom was silent, and the professor began to explain：

“I’m not going to grade (打分) this. I ______ wanted to give you something to think about. No one wrote about the ______ part of the paper. Everyone focused on the black dot, and the same happens in our ______．We have a white paper to observe and ______, but we always focus on the dark spots. Our life is a ______ given to us with love and care, and we always have ______ to celebrate：nature renewing itself every day, our friends around us, the job that ______ our livelihood and the miracles we see every day.

______, we insist on focusing only on the dark spots：the health issues that bother us，the lack of money, the ______ relationship with colleagues, the ______ with a friend, and etc.

The dark spots are very ______  compared to everything we have in our lives, but they are the ones that pollute our minds.”

1.A. handed out    B. wrapped up    C. referred to    D. pointed at

2.A. Since    B. Until    C. If    D. After

3.A. fold    B. turn    C. open    D. use

4.A. exercises    B. choices    C. questions    D. scores

5.A. remember    B. imagine    C. study    D. see

6.A. surprised    B. confused    C. curious    D. displeased

7.A. collected    B. finished    C. marked    D. selected

8.A. excuse    B. doubt    C. exception    D. explanation

9.A. said    B. answered    C. returned    D. read

10.A. also    B. just    C. even    D. finally

11.A. big    B. black    C. beautiful    D. white

12.A. lives    B. classrooms    C. colleges    D. studies

13.A. send    B. keep    C. enjoy    D. show

14.A. burden    B. gift    C. pressure    D. lesson

15.A. reasons    B. time    C. freedom    D. festivals

16.A. threatens    B. ruins    C. provides    D. changes

17.A. However    B. Therefore    C. Besides    D. Moreover

18.A. close    B. complicated    C. special    D. strong

19.A. stay    B. contact    C. satisfaction    D. disappointment

20.A. dark    B. round    C. small    D. dirty