12.
(A) that scientists have experimented for decades
(B) what has been widely used in clinical treatment
(C) which is more potent than traditional painkillers
(D) where cone snail venom is explored and investigated
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統計: A(0), B(0), C(3), D(0), E(0) #3888276
統計: A(0), B(0), C(3), D(0), E(0) #3888276