If water is scarce and energy is abundant, for example, it is easy to desalinate and transport water; if energy is expensive, desalination and transport may be impractical.

• 举例来说，要是水很希罕而能量很丰富，就很容易将海水化淡，运输各地；要是能量很昂贵，淡化海水、运输各地的点子就可能不切实际了。