Answer: The correct answer for the blank is- C. helps a species survive.
Adaptation can be described as process of change in a living organism according to which the organism becomes better suited to the environmental conditions, leading to increase in the chances of survival and reproduction.
According to Natural selection, an evolutionary theory given by Charle's Darwin, organism that can better adapt in the changing environmental conditions survive and increase their number through reproduction, whereas organisms that can not adapt are eliminated from the population eventually.
Thus, option C) is the right answer.