Use of apostrophe

Hi,

The former.

Clive

It's said that we should use 's for living things and shouldn't use 's for non-living things.

Here are a few examples.
(1) Ali's car
(2) Teacher's day
(3) Car lesson

But
(1)today's
(2)the world's largest

However, sometimes it's wrong like the phrase above" the world's largest".
Do anybody know what is the best way to differentiate when should we

Please, please, PLEASE do not simply post the same question over and over if you don't get an answer immediately.

We all have lives. We work, we eat, we sleep. We even... yes, really ... take care of our families. If someone doesn't respond to you right away, posting it again won't make it happen any faster.

A lot of learners are convinced we don't ever use 's on things that are

I post the question again, as I think that if I don't post it again, people may not see it.
I actually know that you all have your own jobs.
I am sorry for causing any troubles

People will see it. Posting it again only -- as you have seen -- makes us angry.

I am so sorry for that!
I think that people may not see the second page of the forum.
So when it was ....to the second page I repost it again.
Futhermore, I think people may misread that thread with a lot of posts were answered so I repost it again.
I feel really sorry for that.