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题目内容双击单词支持查询和收藏哦～
Considering how difficult it is to prove or disprove the existence of life on Mars, which is practically our neighbor, it is quite _____ challenge to do the same for any Earthlike planets that might exist outside our solar system.
- A.a formidable
- B.an impossible
- C.a hopeless
- D.a daunting
- E.an urgent
- F.an immediate
A,D显示答案
以上解析由 考满分老师提供。
