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题目内容
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.
- Aa formidable
- Ban impossible
- Ca hopeless
- Da daunting
- Ean urgent
- Fan immediate
A,D显示答案
以上解析由 考满分老师提供。