Answer: The correct answer for the blank is -
c. Biological control.
Explanation:
Biological control (also known as biocontrol) is considered as one of the most  successful and significant way to control invasive species such as pests and weeds. This method utilise the natural enemies (which can be virus, parasitic or predatory organism, bacteria, fungi) of the invasive species to control them.
Thus, option c) is the right answer.
