Motorcyclists need extra space on
a. wet or icy roads.
b. metal surfaces and railroad crossings.
c. on gravel and pavement seams.
d. all of the above conditions.

necessary and proper clause. the congress shall have power to all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states, or in any department or officer thereof.

nothing certain is known about what happened, but it seems that the country declined gradually, perhaps due to bad government, or, more likely, due to a series of bad harvests, which resulted in widespread and recurrent famine.