We have to prove the scratched blade of sickles on sight one is not necessarily because of harvesting in order to undermine the statement.
(A) Some sickles that have not yet been found at the first site do not have cratched blades.(well, since the unfound sickles are still unknown, how can we be sure about the scrateches being present on blade or not) (Incorrect)
(B) The scratches on the blades of the sickles found at the first site resulted from something other than harvesting grain.(If the scratches on Sight 1 sickles is not because of harvesting, the option will undermine the statement) (Keep this)
(C) Sickles at both sites had ritual uses whether or not those sickles were used to harvest grain. (We want to know whether the scratches are been formed because of harvesting, other rituals are out of context) (Incorrect)
Is
(D) At the second site tools other than sickles were used to harvest grain. (this option introduces new tools, which don't say anything about the sickles scratches) (Incorrect)
(E) The sickles found at the first site were made by the same people who made the sickles found at the second site. (So what? We still need to Determine the scratches source on sight 1, which is not present on sight 2) (Incorrect)
B is the answer.
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