五个不同的数，两两之和依次等于3，4，5，6，7，8，11，12，13，15．这五个数的平均值是()．
A. 18．8
B. 8．4
C. 5．6
D. 4．2
E. 4．8
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已知x1，x2，x3的算术平均值为a，y1，y2，y3的算术平均值为b，则2x1+3y1，2x2+3y2，2x3+3y3是算术平均值为()．
A. 2a+3b
B. (2/3)a+b
C. 6a+9b
D. 2a+b
E. 以上答案均不正确
Poor health amongst Ugandans
A. results from insufficient access to healthcare facilities.
B. can be attributed to poor economic conditions.
C. has resulted in increased mortality rates.
D. All of the above.
Robots differ from automatic machines______after completion of one specific task, they can
A. that
B. which
C. in that
D. in which
Why did Jack say he needed some time to spend with his son？
A. Because he was very tired of his work and wanted to have a good rest.
Because he had promised to spare more time to stay with his son.
C. Because he had missed his son and his family for days.
D. Because he came to realize the importance of the time with his family.
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