题干

已知x2+4y2+kz2=36,且x+y+z的最大值为7,则正数k等于(  )

A:1

B:4

C:8

D:9

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答案(点此获取答案解析)

D

同类题1

根据短文内容,选择正确答案。

                                                                                     C

    Zheng Lin is a Junior 3 student in Shijiazhuang, Hebei. Earlier this month, Zheng and his classmates stood on the street with a box asking people for donations(捐款). Later they gave the money they got to the poor students in their school.

    Many Chinese students raise money to help people in need. Most of the time, they hold a box and ask for donations on the street or in the park. Or they sell things like old books and CDs. Those students have done a great job so far. The money helps the students in poor areas like Yunnan and Gansu with new clothes, pens and pencils.

    Teenagers in the U.S. make donations, too. But they raise money in a different way---they raise money by doing something for others. For example, they sell homemade food or play musical concerts in their neighbourhood to raise money.

     "Chinese students like to wait for people to donate, or sell things that they buy with their parents' money," says Ge Daoshun, an expert. "While U.S. kids get donations and give people something useful in return."

    Ge says Chinese teenagers should learn to raise money in the U. S. kids' ways. "That way, they can show their talents and practice communication. More importantly, they can learn every coin counts(有价值). They have to work hard to get a donation."