Answer:
C. Doctors have been unable to develop a vaccine.
Explanation:
<span>Imperialism runs counter to the idea that everyone should have liberty. When a stronger nation takes over a weaker nation, those who are controlled are now at the whim of the (usually larger and) stronger country. Any actions that the stronger country want to take are now automatically foisted upon the weaker countries, who may not feel that these actions are in their best interests.</span>
Along with amazing technological advances, the Industrial Revolution of the mid-19th century introduced new sources of air and water pollution. By the middle of the 20th century, the effects of these changes were beginning to be felt in countries around the world.
The trogan horse is the answer.
Brainlest answer