问题 选择题

有毒物质通常会通过食物链不断积累。你认为正确表示生态系统中生物体内积累的有毒物质数量多少的图示是

答案

答案:D

题目分析:生物富集作用是指环境中一些有害物质(如重金属、化学农药等),通过食物链在生物体内不断积累的过程.因为这些有害物质具有化学性质稳定、不易分解的特点,会在生物体内积累而不易排出,所以随着营养级的升高而不断积累,危害最大的是这一食物链的最高级消费者.在食物链“草→兔→鹰”中鹰体内积累的有毒物质最多.

阅读理解

阅读理解    

     Mr. Smith, an expert of medicine, was very strict with the students. Every time he took the chair

on the exam committee ( 担任考试委员会 * * ),the students would be worried, for he was seldom

pleased with their answers. A student would be lucky enough if he or she could receive a good mark

(分数) from him. Now a student came into the exam room and sat before the committee. This student

was a little nervous as he knew it would not be so easy for him to pass the exam.    

     The student was asked to describe an illness. His answer was OK. Then Mr. Smith asked about

the cure ( 疗法 ) for the illness, and the student, too, gave a quick answer. "Good," sad Mr. Smith,"

and how much will you give the patient ( 病人) ?""A full spoon," answered the student.   

      " Now you may go out and wait for what you can get," said Mr. Smith. At the same time the

committee discussed the answers the student had given. Suddenly the student realized that there was

something wrong with his last answer. " A full spoon is too much," he thought to himself. Very worriedly

he opened the door of the room and cried, " Mr. Smith, I've made a mistake. A full spoon is too much

for the patient. He can take only five drops." " I am sorry, boy," said Mr Smith coldly. " But it's too late.

Your patient has died."

1. Why were all the students afraid of Mr. Smith?

A. Because he was always strict with them.

B. Because he often laughed at them when they were in trouble.

C. Because he never listened to them carefully when they answered his questions.

D. Because he often misunderstood them and gave them bad marks.

2. What does the underlined word "seldom" in the passage mean?

A. not greatly              

B. not also                  

C. not often                

D. not really 

3. Before he left the room, the student was almost sure that _______.

A. he hadn't done well in the exam

B. he had made a mistake in the exam

C. his answer to the last question was wrong

D. he had passed the exam and the only thing was to wait for the result   

4. From the passage we can learn that the patient would __________.

A. be safe in taking only five drops at a time

B. be in trouble if he took five drops at a time

C. be all right soon if he took one full spoon at t time

D. be not well again without the student's help 

5. We can guess that the student ______.

A. received a good mark at last

B. failed the exam at last

C. passed the exam at last

D. would be no longer afraid of Mr. Smith from them on

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