This strengthens the argument. If the Siberian Clovis points predate any Clovis points found in North America, and we know people went from Siberia to North America, then it seems more plausible that the Clovis point was invented in Siberia before being brought over to North America.

This doesn't strengthen the argument. All this answer choice does for us is give us some kind of a date for the Clovis points found in Siberia: after the land bridge had disappeared. Without additional information--notice that the stimulus doesn't even tell us whether Clovis points have been discovered in North America--this neither strengthens nor weakens the author's main point that the Clovis point was not invented in North America.

Irrelevant. We don’t care how effective Clovis points were. We’re talking about whether they originated in Siberia or North America.

Irrelevant. We’re talking about paleohuman artifacts, not about what happened after paleohumans left. Those artifacts were likely created by different groups.

If anything, this weakens the argument. It provides a possible alternative explanation for how the Clovis points ended up in Siberia, consistent with the belief that the Clovis point was invented in North America: paleohumans brought the Clovis point back to Siberia from North America across the land bridge.