题目内容：
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
参考答案：
选择题：35.Much research _______ into the possible causes
- 题目分类：郑州工程技术学院-大学英语（2）
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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