Nice sentence! I need 20 characters or more so yay me I guess.
The moust important one is the one
The preposition of the sentence would be the word "of" since it relates the subject, the Incas, to the clause, which is "possessions with special knotted cords called quipu."
i would say asking a a question
The pronoun is is because pronouns are such words like,as,IS, and others.
So the pronoun is is