it is 和it was区别?

题目

it is 和it was区别?
It was smart of you to bring a map.
It is stupid of you to tell him the truth.
为什么it is stupid不可以变成it was stupid呢?.两个都是形容词呀?

答案

is和was都是be动词的变形,而不是形容词,be动词最基本的用法是表示事物的状态或者身份.
这两个句子里面因为句子意思导致句子时态的需要,分别选用表示一般现在时的is和一般过去时的was.