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Why don’t birds get lost on their long flights from one place to another Scientists have puzzled over this question for many years. Now they’re beginning to fill in the blanks.Not long ago, experiments showed that birds rely on the sun to guide them during daylight hours. But what about birds that fly by night Tests with artificial stars have proved that certain night - flying birds are able to follow the stars in their long- distance flights.A dove (鸽子)had spent its lifetime in a cage and had never flown under a natural sky. Yet it showed an inborn ability to use the stars for guidance. The bird’s cage was placed under an artificial star-filled sky. The bird tried to fly in the same direction as that taken by his outdoor cousins. Any change in the position of the artificial stars caused a change in the direction of his flight.But the stars are apparently their principal means of navigation(航行)only. When the stars are hidden by clouds, they seemingly find their way by such landmarks as mountain ranges, coast lines, and river courses. But when it’s too dark to see these, the doves circle helplessly, unable to find their way. The reason why birds don’t get lost on long flights ().
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在窗体上画一个名称为Command1的命令按钮，然后编写如下程序： Public Enum S a=4 b=3 End Enum Private Sub Command1 Click() Dim x As Integer x=a If x>=3 Then MsgBox"Pass!" End Sub 运行程序，其结果是( )。
下列叙述中错误的是( )。
Long after the 1998 World Cup was won, disappointed fans were still cursing the disputed refereeing(裁判)decisions that denied victory, to their team. A researcher was appointed to study the performance of some top referees.The researcher organized an experimental tournament (锦标赛) involving four youth teams. Each match lasted an hour, divided into three periods of 20 minutes during which different referees were in charge.Observers noted down the referees’ errors, of which there were 61 over the tournament. Converted to a standard match of 90 minutes, each referee made almost 23 mistakes, a remarkably high number.The researcher then studied the videotapes to analyse the matches in detail. Surprisingly, he found that errors were more likely when the referees were close to the incident. When the officials got it right, they were, on average, 17 meters away from the action. The average distance in the case of errors was 12 meters. The research shows the optimum(最佳的)distance is about 20 meters.There also seemed to be an optimum speed. Correct decisions came when the referees were moving at a speed of about 2 meters per second. The average speed for errors was 4 meters per second.If FIFA, football’s international ruling body, wants to improve the standard of refereeing at the next World Cup, it should encourage referees to keep their eyes on the action from a distance, rather than rushing to keep up with the ball, the researcher argues.He also says that FIFA’s insistence that referees should retire at age 45 may be misguided. If keeping up with the action is not so important, their physical condition is less critical. It can be concluded from the experiment that ().
在窗体上画一个命令按钮(名称为Command1)，并编写下列代码： Function Fun1(ByVa1 a As Integer，b As Integer)As Integer Dim t As Integer t=a-b b=t+a Fun1=t+b End Function Private Sub Command1Click() Dim X As Integer x=10 Print Fun1(Vun1(X，(Fun1(x，x-1)))，x-1) End Sub 程序运行后，单击命令按钮，输出结果是( )。
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