it is time that our goverment did something to prevent water pollution此句中为何用did,不应用does

我在一个叫 "mastering grammar" 的网站上找到有关资料,
--- 以下是在网上找到的资料 ---
我们用 It is time 来表达:现在是时候做某事了.
先讲句子结构.
1) It is time + infinitive:
It's time to start the race.(现在是时候开始比赛了.)
It is time to take a break.(现在是时候休息一会儿了.)
2) It is time + for + object + infinitive:
It's time for us to start the journey.(现在是时候让我们开始旅程了.)
It's time for you to go.(你现在是时候去了.)
3) It is time + for + noun:
It's time for breakfast.(现在是时候吃早餐了.)
It's time for a break.(现在是时候休息一会儿了.)
4) It is time + subject + past subjunctive:
It's time we went home.
It is time he came here.
It is time the police took action.
It's time you made up your mind.
请留意,以上4种表达方法意思上不尽相同.
1-3表达的是做某事的时间到了.
而4不单表达做某事的时候到了,更暗示现在才做某事已经有点晚了 (It implies that it's
a little late).要更强调这个意思,可以说 It is high time （现在是非常适当的时候）:
It's high time the government did something to address the issue of wealth inequality in Hong Kong.
It is high time you stopped being foolish!
除了 it is time 和 it is high time,我们还可以说 it is about time（现在是差不多的时候）：
It's about time you started doing this on your own.
It's about time to leave.
It's about time we went home.
It's about time for you to get going.
It's about time the rich did something to help the
poor.
留意以上第4类 (past subjunctive),我们用过去式动词 (simple past)
来说现在应该做却还没有做的事情,那过去式动词不是真正的过去式(虽然写法一样),乃是带有假设意思的过去式,叫做 unreal past 或是 past subjunctive.
--- 以上是在网上找到的资料 ---