24. Initially, Mead and his colleagues thought that because the variant had never been seen before, it must have damaging rather than beneficial effects.
米德和他的同事起初认为,既然这一变异之前从未发现过,那么它一定具有破坏性而不是相反。
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25. STANDING on the Hoover Dam and looking upstream at Lake Mead, America's largest reservoir, the visitor notices a wide, white band ringing the cliffs.
26. STANDING on the Hoover Dam and looking upstream at Lake Mead, America's largest reservoir, the visitor notices a wide, white band ringing the cliffs.