简述过剩空气系数和加热炉燃烧的关系。
题型：问答题 简答题
问题：
简述过剩空气系数和加热炉燃烧的关系。
题型：问答题 简答题
阅读理解。
It's easy to see how the sawfish got its name. These frightful creatures can grow to be more
than 6 meters long. Their bodies are flat and winged, like underwater airplanes. And their noses
are shaped like chainsaws.
Sawfish are food hunters of the sea. When a sawfish is hungry, it waves its sharptoothed snout
(口鼻部) through a group of fish. Then, it lifts its nose and uses its mouth to draw the injured victims.
Hardy (适应力强的) population of sawfish thrived in warm waters along coastlines around the
world for thousands of years. Over the past 200 years, however, human actions have severely
endangered sawfish. Threats include fishing nets that trap the huge animals, often by mistake.
Some people collect sawfish's snouts as prizes: One snout recently sold for nearly $1,600 online.
In some Asian cultures, the toothy snouts are used in ceremonies to drive evil and disease away. And
sawfish are also delicious. A growing demand in Asia for the fish's fins for a pricey soup has contributed
to the fish's disappearance. Compared with other fish, sawfish give birth late in life and at slow rates,
which makes it hard for them to recover from overfishing.
New efforts now aim to restore sawfish population. Beginning next month, an international agreement
will provide protection for all seven of the world's sawfish species. Scientists are hoping that it's not too
late to save the sawfish.
"Until 1998, this fish had never been formally studied in the United States," says Tonya Wiley of the
Mote Marine Laboratory in Sarasota, FIA."We didn't know such basic things as where they live, what
habitat they use, how often they breed, how many young they have- even what age sawfish are when
they begin breeding."
Through historical studies and field research, scientists have become aware of how much the fish's
numbers have decreased. Today, there may be 90 percent fewer sawfish than there used to be. Wiley
estimates that only 3,000 to 6,000 sawfish remain in US waters.
Sawfish
