Based on your knowledge why are partisanship and a two party system significant parts of us politics

Because there are only two major parties, US citizens feel that they only have a choice between one party or the other.

Because there are only two major parties, the parties tend to disagree greatly on many issues, taking either one extreme side of the argument or the other.

At times, there have been attempts to create a viable third party, but these parties rarely have enough support to be on an equal footing with the two main parties.

the 9th amendment

explanation:

no one really purchased it themselves, it was all america, they had debates etc.