问题
单项选择题
DES算法密钥是64位，因为其中一些位是用作校验的，密钥的实际有效位是（）位
A.60
B.56
C.54
D.48
答案
参考答案：B
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DES算法密钥是64位，因为其中一些位是用作校验的，密钥的实际有效位是（）位
A.60
B.56
C.54
D.48
参考答案：B
阅读下面短文，掌握其大意，从每题所给的A、B、C、D四个选项中，选出最佳选项。 There was a boy who was walking home from school when he saw a large, tempting (attracting) apple on one of the branches of an apple tree hanging out over a tall fence. The boy wasn’t much of a fruit-eater, _36_ a bar of chocolate if given the choice, _37_, as they say, the forbidden fruit can be tempting. Seeing the apple, the boy wanted it. The more he looked at it, the _38_ he felt and the more he wanted that apple. He stood on tiptoe, _39_as high as he could, but even at his tallest _40_he was unable to touch it. He began to _41_ up and down, as high as he could, at the _42_of each jump stretching his arms to get the apple. Still it remained out of _43_. Not giving up, he thought, if only he had something to _44_on. His school bag wouldn’t give enough height and he didn’t want to _45_the things inside, like his lunch box, pencil box, pencil case, and Gameboy. Looking _46_, he hoped he might find an old box, a rock, or, _47_ luck, even a ladder, but it was a tidy neighborhood and there was nothing he could use. He had tried everything he could think to do. _48_seeing any other choices, he gave up and started to walk_49_. At first, he felt angry and disappointed thinking about how hungry he had become from his _50_, and how he really wanted that apple. The more he _51_like this, the more unhappy he became. _52_, the boy of our story was a pretty smart guy, even if he couldn’t get what he wanted. He started to say to himself, “This isn’t_53_.I don’t have the apple and I’m feeling sad as well. There is _54_ more I can do to get the apple— that is unchangeable —but we are supposed to be able to _55_our feelings. If that is the case, what can I do to feel better?
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