It was so quick and easy. A fourteen-year-old boy ...

It was so quick and easy. A fourteen-year-old boy in Scottsdale, Arizona, put his $50 bill on a color copying machine. Within seconds he transformed $50 into $550, and he was ready to shop. Twenty years ago only a few people had the skills or equipment to make fake money. Today computer, copier, and printer technology is so good that almost anyone can "make" money. With the new technology there is a new kind of casual faking machine. These machines are called casual because they don't have special skills and because they don't need to plan much. The number of bills made by casual fakers on their home or office computer is growing fast. In fact, this number has doubled every year since 1989! There is no way to stop faking 100 percent. But the government has recently found a few ways to make casual faking very difficult. One way is to put very, very small words, called microprints(微型印刷品), in hidden places on the bill. The words are only 6/1000 inch. No one can read them without a magnifying glass, a special glass that makes things look bigger. And they are too small to come out clearly on a copier. If someone copies a bill that has microprints and you look at the copy through a magnifying glass, instead of microprinted words, you will see only black lines. Another way to stop people from making fake money on their home computers is to use special color-changing ink. Money printed with color-changing ink will look green from one angle and yellow from another. Home computers cannot use color-changing ink. So any copies from a home computer will have normal ink and can be noticed quite easily. Additionally, money is made on special paper with very small pieces of red and blue silk mixed in. And on each bill there is a special line that runs from the top to the bottom of the bill. Suppose, for example, that you hold a $20 bill up to the light. If you do this, you can see the line has the words "USA twenty". The line turns red if you put it under a special light. This line and the special paper with red and blue silk are not easy for home computers to copy. The government must try many different ways to stop faking. It needs to keep changing the way money is made because fakers can learn to copy the changes. Today copiers can't copy microprinted words or color-changing ink. But, in a few years, who knows？ 8. You can be sure that the bill is faked when ________.

A、you see microprinted words on the bill

B、you see green ink from one direction and yellow from another on the bill

C、you see a special line on the bill that runs from the top to the bottom and that has such words as "USA hundred"

D、you see normal ink on the bill