时间：2022-09-09 08:48:58
For some animals， two wings just won't do - as was the case for a four-winged dinosaur that lived 130 million years ago. Fossils of the creature were unearthed in China about 10 years ago. Since then， scientists have puzzled over how this dino used its two bonus wings. Now researchers report a likely answer.
In a new study， scientists Justin Hall and Michael Habib and their collaborators suggest the dino tucked its hind wings under its body most of the time. It brought the extra wings out only when it needed to make tricky turns in midair. To make a right turn， the dino would lift its left hind wing， for example.
Hall and Habib， who work at the University of Southern California in Los Angeles， presented the new idea about these dinos at a recent meeting of scientists who research prehistoric animals.
Other scientists had suggested that the dinosaur glided through the air either with all four wings out or with one pair positioned beneath the other， like the wings on a biplane. Scientists are still arguing over whether the dinosaur could flap its wings and stay in the air like birds or just glide gently downward.
The new study suggests a simpler solution to the mysterious function of the four wings. Keeping the back wings tucked away most of the time would have made it easier for the animal to remain aloft， Hall finds. He notes that the feathers on the back legs were arranged in a shape that probably didn't add much lift. Lift is an upward force that acts against gravity.
Keeping two wings hidden away when moving straight ahead would have made the dinosaur more aerodynamic， meaning it would have had a shape that let air flow past more freely. Extended all the time， the extra wings would have slowed the dino by creating resistance from the air. Air resistance， or drag， is the enemy of flight： A raindrop falls faster than a feather because air resistance doesn’t slow the drop down as much as the feather.
Hall and his collaborators studied the dinosaur Microraptor gui. It was the first found to have four wings. But it’s no longer the only one： Since M. gui's discovery， other four-winged dinos have turned up. And their hind wings probably worked the same way， says dinosaur expert Luis Chiappe at the Natural History Museum of Los Angeles County.
1. Fossils of the creature unearthed in China about 10 years ago showed the dinosaur was ____.
A. two-winged B. four-winged
C. two-legged D. three-legged
2. We can infer when the dino was making a left turn in midair， it would lift its ____.
A. right hind wing
B. left hind wing
C. right front wing
D. left front wing
3. “remain aloft” in the fifth paragraph probably means ____.
A. keep balance
B. glide in a right way
C. make tricky turns in midair
D. stay high in the air
4. Which of the following state-
ments is not true？ ____.
A. Air resistance is the enemy of flight
B. Scientists haven’t reached an agreement about whether the dinosaur could flap its wings and stay in the air like birds or just glide gently downward
C. Up to now only one four-winged dinosaur has been found
D. Tucking away the back wings would make the dinosaur more aerodynamic
Tai Chi may reduce falls amongstroke survivors. Compared to survivors receiving usual care or participating in a national （A） f program for Medicare-eligible adults called SilverSneakers?， those practicing Tai Chi had the fewest falls.
"Learning how to find and maintain your balance after a stroke is a challenge，" said an assistant professor at the University of Arizona College of Nursing. "Tai Chi is effective in improving both static and dynamic （1） b ， which is important to prevent falls. Tai Chi is readily available in most USA cities and is （2） r inexpensive."
Stroke survivors experience seven times as many falls each year than healthy adults. Tai Chi has significantly reduced falls in （3） h older adults.
Researchers recruited 89 stroke （4） s for a randomized prospective study outside of a hospital setting. Participants were an （B） a 70 years old， who suffered a stroke on average three years prior to beginning the study.
Among the （C） p ， 30 practiced Tai Chi， 28 took part in usual care and 31 participated in SilverSneakers?. The Tai Chi and SilverSneakers? groups participated in a one-hour （D） e class three times each week for 12 weeks. The usual care group received a weekly phone call and written material about participating in community-based physical （5） a .
During the 12-week trial， there were a total of 34 reported falls in participants' homes mainly from slipping or tripping： five falls in the Tai Chi group； 15 falls in the usual care group； and 14 falls in the Silver Sneakers group. The study results suggest main physical （E） b of Tai Chi are better balance， improved strength， flexibility and aerobic endurance.
（A， B， C， D， E FOR CROSS， 1， 2， 3， 4， 5 FOR DOWN. The first letters of the absents were given）
General Gasslefield， accused of high treason， is sentenced to death by the court-martial. He is allowed to make a final statement， after which he will be shot if the statement is false or will be hung if the statement is true. Gasslefield makes his final statement and is released.
The question： What could he have said？
上期答案
上期Crossword答案
1. health 2. benefits 3. pressure 4. certainty
A. diseases B. factors C. attack D. cancer
E. memory F. supplements
上期Illation答案
It is not possible to guess only three fruits correctly： the fourth fruit is then correct too！ So nobody has guessed three fruits correctly， and 123 - 43 - 39 - 31 = 10 people have guessed four fruits correctly.