In a TV commerical, there's some acting involved, and you have to keep it up for a while, which is more of a challenge.

拍电视广告， 要演戏，要坚持一段时间， 比较有挑战性。

None of the commerical highways of the land or sea, marked with buoys and lamps, fences, and guide-boards, is so unmistakably indicated as are these broad, shining trails of the vanished Tuolumne Glacier and its far-reaching tributaries.

没有一条标有浮标、灯、栅栏和路标的陆地或海上商业高速公路，没有一条像消失的图奥勒米冰川及其深远支流的这些宽阔、闪亮的小径那样清晰无误。