MonarchbutterfliesfromeasternCanadamakethemostamazingjourneyintheinsectworld．Eachyear，thisbutterflytravelsabout3000milestoitswinterhomeincentralMexico．Howcanitflysofar？Andwhydoesitmakethislonganddangerous

Question

Monarch butterflies from eastern Canada make the most amazing journey in the insect world．Each year，this butterfly travels about 3000miles to its winter home in central Mexico．How can it fly so far？And why does it make this long and dangerous trip？Scientists still don't have an answer．
For many years，people in Mexico wondered where the orange-and-black butterflies came from every winter．Then，in 1937，a scientist started to follow and study the butterflies．For the next 20years，he discovered that one butterfly started its journey in Canada．Four months later，it arrived in Mexico．
The length of the butterflies finds their way back to the same place？Another amazing thing is that the butterflies always return to the same area in central Mexico．
How do the butterflies find their way back to the same place？This is an interesting question because only every fourth generation（一代）makes the trip south．In other words，the butterfly that travels to Mexico this year is the great-great-grandchild of the butterfly that traveled there last year．
Each year，four generations of a Monarch butterfly family are born．Each generation of the family has a very different life．The first generation is born in the south in late April．It slowly moves north，reproduces，and then dies．On the trip north，two more generations are born，reproduce，and die．Each of these generations of butterflies is born．This generation has a much longer life．It lives for about eight months．This generation of butterflies makes the amazing journey back to the winter home of its great-great-grandparents．The butterflies spend the winter there，and in the spring they reproduce and then die．Their offspring will be the first generation of the next circle of life．
Today，people are still studying the Monarch butterfly．But they are not clear about everything．
31．How long did it take the scientist to find out that monarch butterflies came from Canada？___
A．eight months         
B．four months       
C．five weeks        
D.20years
32．We know that the___ generation of Monarch butterflies travels back to central Mexico．
A．fourth              
B．second            
C．third             
D．first
33．The underlined word"offspring"in paragraph 5means___．
A．seasons            
B．butterflies          
C．children          
D．parents
34．Which of the following is TRUE according to the passage？___
A．Monarch butterflies spend winter in eastern Canada．
B．The four generations have the same length of life．
C．Some generations die on the way north to Canada．
D．Scientists are clear about everything of the butterflies
35．What is the best title of this passage？___
A．Family of Monarch butterflies．
B．Mystery of Monarch butterflies．
C．Monarch butterflies'birthplace．
D．Monarch butterflies'winter home．

Answer 1

31  D 细节理解题．根据文章：For the next 20years，he discovered that one butterfly started its journey in Canada．可知在接下来的20年里，他发现一只蝴蝶在加拿大开始了它的旅行．所以科学家花了二十年．故选D．
32  A 细节理解题．根据文章：the butterfly that travels to Mexico this year is the great-great-grandchild 可知今年迁徙到墨西哥的是玄孙辈，也就是第四代．故选A．
33  C 词义猜测题．根据文章：The butterflies spend the winter there，and in the spring they reproduce and then die．Their offspring will be the first generation of the next circle of life．可知蝴蝶在这过冬，在春天它们生产、死去．它们的offspring将会成下一个生命环游的第一代．所以可推测出offspring是他们的孩子．故选C．
34  C 细节理解题．根据文章：On the trip north，two more generations are born，reproduce，and die．可知在去北方的行程中，两代黑脉金斑蝶出生了，生产了，死去了．故选C．
35  B 标题归纳题．根据文章：这篇文章主要讲述了黑脉金斑蝶们怎么能飞这么远呢？为什么它们要做这样长途而且危险的旅行？这篇文章主要写的就是黑脉金斑蝶之谜．故选B．