But natural selection swings a sharp edge, and the teen's sloppier moments can bring unbearable consequences.
但是，自然选择是把双刃剑，青少年的草率会带来令人无法承受的后果。
'it's a very clean cut,' said the Rat, examining it again attentively. 'That was never done by a branch or a stump. Looks as if it was made by a sharp edge of something in metal. Funny!'
“伤口很整齐，”河鼠再一次仔细检查他的腿。“绝不会是树枝或树桩划破的。看起来倒像是被什么锋利的金属家伙划的。怪事！”
Using pliers or a pipe wrench to tighten a bolt or nut. This may scar the bolt head or nut creating a sharp edge.
使用钳子或管扳手拧紧螺栓或螺帽。这样可能会刮伤螺栓头或螺帽，从而形成尖锐的边缘。
Keeping a sharp edge on chisels and plane irons is absolutely necessary for the successful and safe use of these tools.
为了使凿刀和刨子好用且安全，必须保证他们的刃足够锋利。
If something has been going on for billions of years, you wouldn't expect a sharp edge.
如果什么东西是存在了亿万年的，那么你就不用期待一个明显的边界。
If something has been going on for billions of years, you wouldn't expect a sharp edge.
如果什么东西是存在了亿万年的，那么你就不用期待一个明显的边界。
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