With definite times we use the past tense, not the present perfect.

对于确定的时间，我们用过去时，而不是现在完成时。

It's not a grain of sand. It cannot be said to exist even in a certain place at a definite time.

电子不是一粒沙，所以我们不能说电子可以在固定时间出现在某个地方。

Next, here with the past simple, we talk about definite times. We say when something happened.

接下来，在这里用简单的过去， 我们谈论确定的时间。 我们说什么时候发生了什么。

So, there's no definite time phrase saying it was at like, 4: 42 yesterday or last Saturday.

所以，没有明确的时间短语说它是在昨天或上周六的 4: 42。

Back in the smallest bedroom, Harry made the offer, careful to phrase it so as not to give any definite time for the handover of the sword.

他们回到那间小卧室，哈利答应了他，尽力避免任何能关于何时给他宝剑的承诺。

Well, today we're going to learn about the definite adverbs of frequency because we'll either know the definite time or the number that something occurs.

好吧，今天我们要学习确定频率副词，因为我们要么知道确定时间，要么知道某事发生的次数。

When we're talking about a specific situation, we're talking about the time that you bought this shirt, so it's a simple past because it's a definite past time.

当我们谈论特定情况时，我们谈论的是你购买这件衬衫的时间， 所以这是一个简单的过去， 因为它是一个明确的过去时间。

Yousef says that open-ended invitations are a bad idea, saying to someone, " Yes, come and stay at my house however long you want, " not giving them a definite time.

Yousef 说不限成员名额的邀请是个坏主意， 他对某人说，“是的，来我家住多久都行， ” 而不是给他们一个明确的时间。