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像质计金属丝底片对比度公式讨论提高对比度的主要途径，并说明通过这些途径提高底片对比度可能会带来什么缺点？

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参考答案：

象质计金属丝底片对比度公式△D=-0.434μpγσ•d/（1+n），提高对比度主要途径及由此带来的缺点：

（1）增大μp值。在保证穿透力的前提下，尽量采用能量较低的射线，得这样会使曝光时间增加。

（2）增大γ值。可选用γ值更高的微粒胶片；由于非增感型片胶片γ值和黑度成正比，也可通过提高底片黑度增大γ值。但高γ值的微粒胶片感光速度往往较慢，需要增大曝光时间，提高黑度也需要增加曝光时间，此外，黑度的提高会增大最小可见对比度△Dmin，对灵敏度产生不利影响。

（3）提高σ值，可选择焦点尺寸小的射源，或增大焦距，这样做也会使曝光时间延长。

（4）减少n值。要减小散射线，就要使用铅窗口和铅屏蔽，这些也将降低工作效率，使曝光时间延长。

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                                                      How to Make a Budget (预算)
     Most likely, you aren't the family breadwinner. But doing a small job or getting a weekly allowance (零花钱)
would put some money in your pocket. For kids and grown-ups alike, money is easy to spend. If you aren't
careful, it can be gone in no time. Being responsible with your money is an important skill to learn－and the
sooner you start the better. Whether you are tracking your spending or saving for something special, creating
a budget can help you deal with your expenses and plan for the future. All you need are paper and a pencil－and
some self-control. First, take a look at our sample monthly budget. Then, use a separate sheet of paper to plan
your own. In the first two columns (栏), list your sources (来源) of income and how much you expect to earn
form them. In the third and fourth columns, list what you expect to spend your money on and the amount.
    The left-hand total should
be more than or equal to the
right-hand total. If it is, you
have an effective budget.
     Budgets are not complex,
but sticking to them can be
tough. When planning your
budget, be realistic about
your expenses. If you know		                                       Sample Monthly Budget
Monthly IncomeAmount    Monthly Expenses Amount
Allowance$ 20.00Snacks $ 26.00
Money earned
Selling drinks		$ 25.00Music downloads$ 12.00
Money earned
babysitting		$ 12.50Movies$ 18.00
Money earned $ 30.00 Video rentals $ 10.00
that you drop $ 18 at a movie, don't write $ 12 in that space simply because you wish you were spending less.
     If you are eyeing a big purchase, such as a $ 150 skateboard, spend less and save more until you have the
total amount. No matter how attractive it may be, avoid spending your savings. One day, you will thank yourself?
1. Who is the passage written for?
A. Children
B. Parents.
C. Breadwinners.
D. Bank managers.
2. The purpose of making a budget is to help people ______.
A. learn to be realistic
B. increase their savings
C. manage their money well
D. test their power of self-control
3. What should people do when planning a budget?
A. Fill in the expenses as they really are.
B. Avoid spending money on expensive things.
C. Set aside a fixed amount of money as savings.
D. List income and expenses on two pieces of paper.
4. Which of the following budgets is effective?
A.
B.
C.
D.
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判断题

建筑脚手架的构架杆件，均制成圆形和方形的空心杆件。（）
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