I can suggest some sentences:
1) you can describe what it was:
Manifest Destiny was the belief that settling in America was a destiny, or right, of the settlers.
2) you can describe its effect:
Manifest Destiny was a belief that justified many injustices towards the indigenous people because it suggested that the settlers had a right for the land, which in turn undermined the indigenous claim to the land.
The correct answer is observational learning.
Observational learning refers to the phenomenon where individuals "learn" how to behave by observing others and modelling or imitating their behavior. In Albert Bandura's famous "Bobo doll" experiment, children were made to observe adult role models pounding and being physically aggressive with inflatable Bobo dolls. After that, Bandura investigated whether children showed aggression due to observational learning.
