Why is it important that alien grass, trees, and other plants choked out native vegetation?

Which two important economic activities in the west are possible because of the united states natural resources

Ineed a summary over thurgood marshall ! me

Which of the following is an example of the pull factor known as economic migration? a. better educational opportunities pulling people towards a new country b. mexican laborers entering the us to work in agricultural jobs c. joining family members that are already in a new country d. crop failures driving people away from their country i am unsure on this question, i was thinking b? but i could be wrong.