Answer: The correct answer for the blank is -
strip mining.
Strip mining can be described as a process of mining in which overlying vegetation (such as bushes and trees) is first removed, which is followed by stripping/removal of soil and underground layers of rocks (using scrapers/buldozers and loaders) so as to expose and then extract the coal from the underground deposits of coal.
Thus, strip mining is the right answer for the blank.
