What American argued that overseas expansion was a "safety valve" to keep ambitious Americans content?

Frederick Jackson Turner argued that overseas expansion was a "safety valve" to keep ambitious Americans content.

d is correct the right of the people to be drafted into the armed forces.

hope this let me know if it is right.

the answer to fill in the blank in this question would be the word resource, it is defined as the money, material or people (since human resource is a very valuable good) that a company or a person has at disposition (meaning they can use the resource as they see fit), to be able to complete a task or achieve a goal.