平行单色光垂直入射到单缝上，观察夫朗和费衍射。若屏上P点处为第2级暗纹，则单缝处波面相应地可划分为几个半波带
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逻辑加法的运算规则有（ ）。
A. 0+0=0
B. 0+1=1
C. 1+0=1
D. 1+1=10
1.Which of the following is an example of the unethical use of computers?
A.Employees failing to answer a large number of e-mail messages due to network problems.
B.Employees searching organizational databases for information on celebrities and friends.
C.Employees sending messages without spell checking and proofreading them.
D.Employees updating their passwords at the end of every month.
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