To support revising the Articles of Confederation was that the central government lacks power or lack of centralized government power.
The previous Article of Confederation allowed the states to hold most of the power, and the central government was too weak to even function properly. Due to this there was also huge difference in terms of economics from state to state.
Possible sickness. And multiple death situations.
The senate and the upper class exercised that. A direct democracy is when people vote directly for each and every vote and law, in a representative democracy the people vote for other people to do that.
A. Muslim mathematicians introduced algebra into the world
is correct - that is the reason why the number system we use today is the Arabic Numericals.
B. Ibn Sina collected medical knowledge into a book that was used for centuries in Europe
is correct - that books is called The Canon of Medicine.
