In a study on the biological bases of learning, lab rat a is given a drug that blocks dopamine activity in its brain. thereafter, the rat is placed in an operant chamber where a lever-pressing task is shaped through positive reinforcement. we should expect that the rat will have

We should expect that the rat will have have more difficulty in learning the task compared to a normal rat. This is because the rat has been injected with a certain drug that oppresses the dopamine activity. And then the rat is placed in an operant chamber where a lever-pressing task is shaped through positive reinforcement. 

We can plant more trees and plants.