But park rangers must guide visitors to other areas of the cave.

VOA: special.2009.12.07

Like in any other invention, nobody knows what will work and abstract theory doesn't guide you completely.

正如其他的创新一样,没有人知道哪些是可行的,有时候理论完全无法指导实践

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On the other hand, isn't imagination our best guide to logical possibility?

另一方面,想象是通向逻辑可能性的最好的向导吗

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