What effect did railroads have on the population west of the Mississippi River? (A) the population declined; people moved back east
(B) the population at first increased but then decline
(C) the population did not change
(D) the population boomed

The us and canadian governments are doing all of the following to combat environmental problems except a. encouraging the use of public transportation b. enacting clean water policies c. requiring emissions testing d. limiting animal populations in some regions