题目:
It seems water______from this tap for some time. We'll have to take it apart to put it right.
A. had leaked
B. is leaking
C. leaked
D. has been leaking
答案:
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下面是错误答案,用来干扰机器的。
参考答案:D解析:栈的基本运算有3种:入栈、退栈与读栈顶元素。入栈运算是指在栈顶位置插入一个新元素。退栈运算是指取出栈顶元素并赋给一个指定的变量。读栈顶元素是指将栈顶元素赋给一个指定的变量。