题目内容：
请阅读短文。Anne Whitney, a sophomore at Colorado State University, first had a problem taking tests when she began college. "I was always well prepared for my tests. Sometimes I studied for weeks before a test. Yet I would go in to take the test, only to find I could not answer the questions correctly. I would blank out because of nervousness and fear. I couldn't think of the answer. My low grades on the tests did not show what I knew to the teacher." Another student in biology had similar experiences. He said, "My first chemistry test was very difficult. Then, on the second test, I sat down to take it, and I was so nervous that I was shaking. My hands were moving up and down so quickly that it was hard to hold my pencil. I knew the material and I knew the answers. Yet I couldn't even write them down! "
These two young students were experiencing something called test anxiety. Because a student worries and is uneasy about a test, his or her mind does not work as well as it usually does. The student cannot write or think clearly because of the extreme tension and nervousness. Although poor grades are often a result of poor study habits, sometimes test anxiety causes the low grades. Recently, test anxiety has been recognized as a real problem, not just an excuse or a false explanation of lazy students.
Special university advising courses try to help students. In these courses, advisors try to help students by teaching them how to manage test anxiety. At some universities, students take tests to measure their anxiety. If the tests show their anxiety is high, the students can take short courses to help them deal with their tensions. These courses teach students how to relax their bodies. Students are trained to become calm in very tense situations. By controlling their nervousness, they can let their minds work at ease. Learned information then comes out without difficulty on a test.
An expert at the University of California explains: "With almost all students, relaxation and less stress are felt after taking our program. Most of them experience better control during their tests. Almost all have some improvement. With some, the improvement is very great."
To “blank out”is probably__________.
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A．to be like a blanket
B．to be sure of an answer
C．to be unable to think clearly
D．to show knowledge to the teacher
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