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.
O A. A positive tone
OB. A critical tone
O C. A disgusting tone
D. A joking tone