问题 选择题

经过空间一点P作与直线l成45°角的直线共有(  )条.

A.0

B.1

C.2

D.无数

答案

分为两种情况考虑:

①若点P在直线l上,如图所示:

过直线l上的点O(不同于点P)作AB⊥l,且满足OA=OB=OP,则∠OPA=∠OPB=45°,因此圆锥的任意(无数)一条母线所在的直线与直线l所成的角都为45°;

②若点P不在直线l上,则可过点P作直线ll,同(1)可知:有无数条直线与直线l成45°角,即与直线l也有无数条直线成45°的角.

综上可知:经过空间一点P作与直线l成45°角的直线共有无数条.

因此选D.

填空题
阅读理解

The early 1900s were very different from today, when toys were still the delight of children everywhere.

Theodore Roosevelt's Presidency marks the beginning of the “Teddy Bear”. In the year 1902,toy bears were named “Teddy” after the president's nickname. The Teddy Bear became known worldwide and it was only a few years later that the Teddy Bears were mass produced.

In 1913,an item called the Erector Set was invented. It was a steel,motorized toy that children could use to build models of anything. Its creator was A.C.Gilbert,a medical doctor.

Charles Pajeau created a similar wooden set called Tinker Toys in the year 1914.Tinker Toys were made for younger children.

Raggedy Ann dolls first came on the scene after newspaper cartoonist Johnny Gruelle reproduced the doll he made for his daughter. That was in 1915.

The following year,an architect's son named John Lloyd Wright,invented Lincoln Logs,which were interlocked to make structures.

Two years after Mickey Mouse was created,stuffed(填塞)Mickey Mouse dolls were made by Charlotte Clark. This was the start of Disney merchandise.

The yo­yo became popular in the United States after Donald Duncan bought a yo­yo company in 1929.

The View­Master,a three dimensional viewer,was developed by a camera enthusiast named William Gruber. The toy became popular when Gruber licensed Disney characters to make still, 3­D images from Disney movies and television programs.

Finally,in 1940,model airplanes were mass produced. They started out as a way for manufacturers to sell planes to the military,but later caught on as a toy.

The toys that we know and love today have had their roots from these ancient times. Thanks to all these creative man’s efforts, we know otherwise what we may never know.

小题1:Why were toy bears named “Teddy”?

A.To be suitable for mass production

B.To be easily pronounced by children.

C.To meet the advertisers' needs.

D.To memorize President Theodore Roosevelt小题2:In which aspect do the toys created by Gilbert differ from those by Charles?

A.Shape

B.Material used

C.Themes

D.Price小题3:When did the View­Master become popular?

A.After William Gruber was born

B.After Gruber licensed Disney characters

C.Two years after Mickey Mouse was created.

D.When Disney merchandise was started