问题
选择题
若正整数a，b，c是一组勾股数，则下列各组数一定还是勾股数的是（ ）
A．a+1，b+1，c+1
B．a2，b2，c2
C．2a，2b，2c
D．a-1，b-1，c-1
答案
根据勾股数的概念知，若有a2+b2=c2，则（2a）2+（2b）2=（2c）2也成立，其它三个不成立，故选C．
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若正整数a，b，c是一组勾股数，则下列各组数一定还是勾股数的是（ ）
A．a+1，b+1，c+1
B．a2，b2，c2
C．2a，2b，2c
D．a-1，b-1，c-1
根据勾股数的概念知，若有a2+b2=c2，则（2a）2+（2b）2=（2c）2也成立，其它三个不成立，故选C．
A) 根据所读内容，在文章后第62—71小题的空格里填入恰当的单词。每个空格只填1个单词。  How important is homework? According to the Los Angeles Unified School District(LAUSD), it’s not that important! The district has made a big change for the 2011-2012 school year. It started on July 1, homework counts for only 10% of a student’s grade. The district, the second largest in the country, says its new way can provide a fairer assessment(评定) of students’ homework and achievements. The district hopes students only need to spend less time on homework and more time on hobbies and with their families. By reducing the weight of homework toward a student’s grade, a truer picture of the student’s knowledge will be shown in the achievement grade. However, it doesn’t mean the students can throw out homework. It says that homework is a chance for students to practice their skills and a tool for students to prepare for coming lessons. Still, LAUSD is joining a growing list of schools that have controlled the amount of homework. How much time children should spend on homework is a hot topic. Harris Cooper, a professor at a university, says that the proper amount of homework time is ten minutes a day multiplied by(乘以) the student’s grade. This means a third grader should spend 30 minutes a day on homework. And a sixth grader would spend 60 minutes. “Good homework in the proper amount will have better effects on them,” he said. “Bad homework or too much homework will have worse effects.” But some people think homework is an important part of learning. They say many children just won’t try their best if homework doesn’t count toward their grade. Some teachers also think homework is important. They argue that students who do their homework perform better on tests and in school than those who do not. They are afraid that the new way will encourage students to pay less attention to homework.
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