问题 选择题

玉米、水稻和马的体细胞中的染色体数分别是20、24和64条,它们产生的精子和卵细胞中的染色体数目分别是

A.20、24、64

B.40、48、128

C.10、12、32

D.5、6、16

答案

答案:C

题目分析:体细胞中染色体是成对存在,在形成精子和卵细胞的细胞分裂过程中,染色体都要减少一半.而且不是任意的一半,是每对染色体中各有一条进入精子和卵细胞.生殖细胞中的染色体数是体细胞中的一半,成单存在.当精子和卵细胞结合形成受精卵时,染色体又恢复到原来的水平,一条来自父方,一条来自母方.如玉米、水稻和马的体细胞中的染色体分别为20、24、64条,它们产生的精子或卵细胞中的染色体数分别是10条、12条、32条。

选择题
阅读理解

阅读理解。

     MONTREAL (Reuters)-Crossing the US-Canada border (边界) to go to church on a Sunday cost a US citizen $10,000 for breaking Washington's strict new security(安全) rules.The expensive trip to church was a surprise for Richard Al-bert, who lives right on the Canadian border. Like the other half-dozen

people of Township 15, crossing the border is a daily occurrence for Albert. The nearby Quebec village of St. Pamphile is where they shop, eat and go to church.    

     There are many such situations in these areas along the largely unguarded 5,530 mile border between

Canada and the US which in some cases actually runs down the middle of streets or throughbuildings.    

     As a result, Albert said he did not expect any problems three weeks ago when he returned home to the US after attending church in Canada, as usual. The US customs (海关) station in this area is closed on

Sundays, so he just drove around the locked gate, as he had done every weekend since the gate appeared last May, following a tightening of border security. Two days later, Albert was told to go to the customs

office, where an officer told him he had been caught on camera crossing the border illegally(非法).    

     Ottawa has given out special passes to some 300 US citizens in that area so they can enter the country when Canadian customs stations are closed, but the US stopped a similar program last May.That forces

the people to a 200 mile detour along hilly roads to get home through another border check point.    

     Albert has requested that the customs office change its decisions on the fine, but he has not attended a Sunday church since. "I feel like I'm living in a prison," he said.

1. We learn from the text that Richard Albert is_______.    

A. an American living in Township 15    

B. a Canadian living in a Quebec village    

C. a Canadian working in a customs station    

D. an American working in a Canadian church

2. Albert was fined because he_______.    

A. failed to obey traffic rules    

B. broke the American security rules    

C. worked in St. Pamphile without a pass    

D. damaged the gate of the customs office

3. The underlined word " detour" in Paragraph 5 means______.    

A. a drive through the town    

B. a race across the fields    

C. a roundabout way of travelling    

D. a journey in the mountain area

4. What would be the best title for the text?   

A. A Cross-country Trip.    

B. A Special Border Pass.    

C. An Unguarded Border.    

D. An Expensive Church Visit.