Answer: Option D
Step-by-step explanation:
The unwelcome species or the invasive species can be stopped by entering into a new place by killing them at proper time.
They can be prevented from entering into a new place by various means, they can also be stopped from reproducing and giving birth to new ones so that they cannot conquer the area.
They can be killed once they are found and these are some of the ways by which they can be prevented from entering into a new place.