6. The satellite dish receives satellite television signal and decodes it for the TV screen.
7. Satellite TV has encountered fierce competition from digital cable， which also has improved picture quality and extended channel selection.
[Y][N][NG] 2. [Y][N][NG] 3. [Y][N][NG]
4. [Y][N][NG] 5. [Y][N][NG] 6. [Y][N][NG]
7. [Y][N][NG]
8. Satellite television is similar to broadcast television in the way that is for sending television programming directly to a viewer‘s home.
9. In the United States， the two major providers of direct broadcast satellite television are
10. The satellite television signal is transmitted in the digital video format of
Passage 5
DNA Evidence
What if there were a way of tying a person to the scene of a crime beyond a shadow of a doubt？ Or， more importantly， what if you could nde out suspects and prevent the wrong person from being locked up in jail？ This dream is beginning to be realized through the use of DNA evidence.
Your Own Personal Barcode
We all like to think that we are unique， not like anyone else in the world. Unless you are an identical twin， at the nuclear level， you are！ Humans have 23 pairs of chromosomes containing the DNA blueprint that encodes ali the materials needed to make up your body as well as the instructions for how to run it. One member of each chromosomal pair comes from your mother， and the other is contributed by your father.
Every cell in your body contains a copy of this DNA. While the majority of DNA doesn‘t differ from human to human， some 3 million base pairs of DNA （ about 0.10 percent of your entire genome） vary from person to person. The key to DNA evidence lies in comparing the DNA left at the scene of a crime with a suspect’s DNA in these chromosomal regions that do differ.
Creating a DNA Profile
The basic procedure used to isolate an individual‘s DNA fingerprint is called Restriction Fragment Length Polymorphism （RFLP） analysis. This is a complicated way of saying that investigators determine the number of VNTR repeats at a number of distinctive areas to come up with an individual’s DNA profile.
For each person， there are two numbers of repeats in each VNTR region （ one from mom and one from dad）， so you are getting both counts， ff you do this for a number of different VNTR regions， you can build a profile for a person that is statistically unique. The resulting DNA fingerprint can then be compared with the one left by the "perp" at a crime scene to see if there might be a match.
Advances in DNA Evidence
In 1985， DNA entered the courtroom for the first time as evidence in a trial， but it wasn‘t until 1988 that DNA evidence actually sent someone to jail. This is a complex area of forensic science that relies heavily on statistical predictions； in early cases where jurors were hit with reams of evidence heavily laden with mathematical formulas， it was easy for defense attorneys to create doubt in jurors’ minds. Since then， a number of advances have allowed criminal investigators to perfect the techniques involved and face down legal challenges to DNA fingerprinting. Improvements include：
。 Amount of DNA needed――using the polymerase chain reaction （ PCR ）， investigators now only need tiny amounts of a specific DNA sequence for analysis.
。 Source of DNA――Science has devised ingenious ways of extracting DNA from sources that used to be too difficult or too contaminated to use.
。 Expanded DNA databases――Several countries， including the U.S. and Britain， have built elaborate databases with hundreds of thousands of unique individual DNA profiles. This adds a lot of weight to arguments formerly based on mathematical theory alone.
。 Training――Crime labs have come up with formal protocols for handling and processing evidence， reducing the likelihood of contamination of samples. On the courtroom side， prosecutors have become more savvy at presenting genetic evidence， and many states have come up with specific rules governing its admissibility in court cases.
发表于 2016-7-11 18:40:35