Please help me :( this is too hard here:

Why is it useful for historians to base certain studies on the analysis of historical periods

How are diamonds and graphite the same? how are they different? a. both diamonds and graphite are made entirely out of carbon. they are different because the carbon atoms are arranged differently with a more three-dimensional structure in diamonds and flat layers in graphite. b. both diamonds and graphite have atoms that are arranged with flat layers. they are different because only graphite are made entirely out of carbon. c. both diamonds and graphite have atoms that are arranged with three-dimensional structures. they are different because only diamonds are made entirely out of carbon. d. diamonds and graphite have no similarities. they are different because the carbon atoms are arranged differently with a more three-dimensional structure in diamonds and flat layers in graphite.

How is the president involved in the process of bills becoming laws?