每日一题

012. The ocean bottom --- a region nearly 2. 5 times greater than the total land area of the  Earth --- is a vast frontier that even today is largely unexplored and uncharted, until about a  century ago, the deep-ocean floor was completely inaccessible, hidden beneath waters  averaging over 3,600 meters deep.  The word "inaccessible" is closest in meaning to which of following?