题文
The research is so designed that once __________ nothing can be done to change it.
| A.begins |
| B.having begun |
| C.beginning |
| D.begun |
推荐试卷
The research is so designed that once __________ nothing can be done to change it.
| A.begins |
| B.having begun |
| C.beginning |
| D.begun |
试题篮
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