What is the preposition of this sentence: the incas kept records of their possessions with special knotted cords called quipu.

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."

Iwould say “longest” i could be wrong thoughof the two roads, i’be always taken the longest one.