若一个栈以向量V[1..n]存储，且空栈的栈顶指针top为n+1，则将元素x入栈的正确操作是（） 。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;
