B) At all camps in the region that have been reliably dated to the late 1620's, remains of European trade goods have been found.
In logic terms: If [camp later than late 1620's], then [European goods found].
The countrapositive: If [European goods are NOT found], then [camp are NOT later than late 1620's].
Therefore, (B) supports the claim that the camp probably dates to no later than 1630 [the same as LATE 1620's].
-- by 会员 sdcar2010 (2011/1/7 22:07:14)