单项选择题

材料的电阻率与掺杂浓度有关,掺杂浓度越高,电阻率越低,电导率就越高。( )

A.对
B.错
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问答题

Directions: Read the following passage. After reading it, you are required to complete the outline below it. You should write your answers briefly in no more than three words.
 
Passage2
 
                                                                                                                                                 December 10th, 2018
Dear Sirs,
    I know that your company has a reputation(声誉) for quality products and fairness toward its customers. Therefore, I'm writing to ask for a replacement for a lawn mower (割草机).
    I bought the mower about half a year ago at the Watchung Discount Center, Watchung, Nebraska. I'm enclosing a copy of a receipt for the mower.
    A month after I bought the lawn mower, the engine failed, and it was repaired under warranty(保修期). So far, I have had the engine repaired four times.
    Now the engine has broken down again.
    I have already spent more than $ 300 on repairs, and I am beginning to seriously question the quality of your mowers.
    I am requesting that you replace this mower with a new one.
    I hope that you will live up to your reputation of the good customer service that has made your business successful.
 
Faithfully,
Rod Green
 
Letter of Complaint
Purpose of the letter: requesting a             for a lawn mower
Time of purchase: about    (17)      age
Trouble with the machine:         
Times of repairs so far:           
Money spent on repairs: more than

答案: half a year
问答题

250mH=         H

答案: 0.25
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