I think the key is to clear the relation between projectile and Eurasian. The human-made projectile shows no similarity of Eurasians artifacts near North American.

A says the projectile found does not resemble any were used in Eurasia, thus, no matter near or far from North America, it can not be concluded that the first settlers came from a more distant area part of Eurasia.

BE no relate to projectile, CD no weaken the conclusion.

I am planning to take the Nov test, study in the early morning before I go to work recently, want to join you~