lesson 21 短听力：听一遍录音，选择最佳答案。
At FL 360 or below.
B. Ahead and above FL 380.
C. Request descent to FL 360.
D. Ahead and below FL 380.
What is the main idea of the news?
A. The mercury level in fish decreases appreciably.
B. The mercury level in fish can be tested very quickly.
C. The mercury level in fish is much higher than we think.
D. The mercury level in fish cause millions of deaths in the world.
What new technology has the California company come up with?
A. It can test the mercury level in a particular piece of fish in 40 seconds.
B. It can test the mercury level in human in 40 seconds.
C. It can test the mercury level in a particular piece of fish in 45 minutes.
D. It can test the mercury level in human in 45 minutes.
Why does the FDA say that the mercury labeling is unneccesary?
A. Because the pulic isn't interested in it.
Because the labeling is not always accurate.
C. Because the mercury labeling will panic the pulic.
D. Because all the fish sold at the grocery stores is tested and healthy.
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