Which of the Following Populations Would Be Most Vulnerable to an Outbreak

Which of the following populations would be most vulnerable to an outbreak of disease?

A) 10 grasshoppers living in an area of 100 square meters
B) 100 rabbits living in an area of 10,000 square meters
C) 200 sparrows living in an area of 20,000 square meters
D) 250,000 people living in an area of 100,000 square meters