Can someone please help me​

Why did some states believe they had the power to overturn federal laws?

How did the completion of the transcontinental railroad change the lives of american citizens? a-it increased the wealth of all americans and enabled them to travel more. b-it made cross-country travel too expensive for ordinary americans. c-it decreased the safety of americans who moved to settle the plains. d-it shortened travel time between the east and west for all americans.

Following archduke franz ferdinand's assassination, austro-hungarian leaders: a. aided the ottoman empire in its campaign to keep serbia under its control. b. executed nearly all prominent serbs living in austria-hungary c. threatened to invade serbia if serb leaders did not agree to a set of strict demands. d.. formed an alliance with great britain to protect austria-hungary from future attacks.