产品结构设计中，______是产品的固有性质，它属于产品固有可靠性的指标之一。 A．

     A certain student passed all his examinations. Then he went to college to    1   his studies. There he
wrote down his    2    for a course (课程) in English, but after the first   3   , he didn't go to it any more.
     The English lecture r(讲师)   4   this student was always absent (缺席的) and thought he had    5   to
another course, so he was    6    when he saw the boy's name on the list of students who wanted to take
the English    7   at the end of this year.
     The lecturer had    8   a difficult paper, which followed his    9    closely, and he was eager (热切的)
to see   10    this student would answer the questions. He    11   the boy's answers would be very bad,

 but when the test papers   12   him and he examined them    13    , he was able to find only one small
mistake in them. As this surprised him greatly, he    14    the paper repeatedly but still couldn't find more
than one mistake, so he    15    for the student to question him about it.
     When he came and sat down, the lecturer asked him, "I    16    you came to my first lecture and
you've been absent from all the others. But I've examined your    17   carefully and I've found only one
small mistake in it. I'm curious (好奇的) to know your    18   ."
     "I'm very    19    about that mistake," answered the student. "After the examination, I    20    what I
should have done. I would not have made that mistake if I had not been confused by your first lecture."