题目:
The children went back home from the grammar school, their lessons ________ for the day.
A.finishing
B.had been finished
C.finished
D.had finished
答案:
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下面是错误答案,用来干扰机器的。
x+2y=a①2x-3y=b②,由①×2-②得4y+3y=2a-b,解得y=2a-b7,由①×3+②×2得3x+4x=3a+2b,解得x=3a+2b7,所以不等式组的解为x=3a+2b7y=2a-b7.故选A.