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题目内容
（郑州工程技术学院-大学英语（2））
35.
Much research _______ into the possible causes of the disease in the past few years.
(A) has been done
(B) was done
(C) have been done
(D) were done
Much research _______ into the possible causes of the disease in the past few years.
(A) has been done
(B) was done
(C) have been done
(D) were done
参考答案