几十年以来，这种畏惧感经历了阴晴圆缺，但关于它们安全性的问题还在争论当中。
Over the decades, the fears have waxed and waned, but questions about their safety are still debated.
其他的回答指出这个问题本身就是矛盾的，就像“正方形的圆”一样。
Other answers include the question being a contradiction, like a “square circle”.
如果找一个这个问题中的向量场，然后我们要做的是，假设这个单位圆。
Well, if I take the vector field that was in the problem set, and if I do things, say that I look at the unit circle.
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