Boats could carry heavy weights, but canals could not cross hilly terrain; turnpikes could cross the hills, but the roadbeds could not stand up under great weights.
船可以运载重物，但运河不能穿越丘陵地带；高速公路可以翻山越岭，但路基承受不了巨大的重量。
2
Guitarists now worry that every time they cross a state border with their instrument, they will have to carry sheaves of documents proving that every part of it was legally sourced.