What method do researchers use when they need to exert significant control over what happens in their study

Read the list of selections from the article. trump still seeks a border wall and said he might shut down the government again over it. a strong majority of americans blamed him for the standoff. and they rejected his arguments for a border wall, recent polls show. it is not clear how trump would fund the wall by declaring a national emergency. minutes later, senators voted 52-44 for a democratic plan to open agencies through february 8 with no wall money. that was eight votes short. yet it got more support than trump's republican plan, even though republicans control the senate 53-47. which two selections, taken together, provide the best evidence to support the idea that most people do not support funding a border wall? a 1 and 3 b 1 and 4 c 2 and 3 d 2 and 4

Restricting immigrants from entering a country may be based on what belief?  

This was an act of continental congress which initially organized the first united states territory and was to be the basis for governing how the united states would expand westward.