若一個棧以向量V[1..n]存儲，且空棧的棧頂指針top為n+1，則將元素x入棧的正確操作是（） 。A.top = top+1; V[top] = x; B.V[top] = x; top = top+1; C.top = top-1; V[top] = x; D.V[top] = x; top = top-1;
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