The rising and falling water level entails various consequences. One of the most obvious, well known to all who have seen Lake Mead, is the "bathtub ring" left on the canyon walls after each drawdown of water, or what rangers at Glen Canyon call the Bathtub Formation. This phenomenon is perhaps of no more than aesthetic importance; yet it is sufficient to dispel any illusion one might have, in contemplating the scene, that you are looking upon a natural lake. A. A joking tone O B. A critical tone C. A positive tone D. A disgusting tone​