载人宇宙飞行的前景看上去充满了越来越多的变数。The future for manned space flight is looking increasingly uncertain.作为摩托车初学者，切勿后座载人。As a learner rider you must not carry a pillion passenger.载人的潜水器与宇宙飞船一样, 必须在非自然的环境下保持生存条件.Manned submersibles, l...
Scientists have discovered that most of the active volcanoes in the world are located in a T-shaped area.科学家们发现,世界上大部分活火山都位于一个T形地区里。Hawaiian volcanoes are among the most thoroughly studied and systematically monitored ac...