Why did the Founding Fathers choose a federation plan of government?

i will need the answers to the problems. i took the test but cant remember the options. i would look up the questions that might .

for number 3, the answer is something about how they wanted to get sc to vote twords it, so they add the bill of rights or edited it.

for number 5, the answer is that it was even, they chose one side just as likely as they did the other.