GUIDE ENGLISH GRAMMAR BOOK

20 POSSESSIVES AND DEMONSTRATIVES PAGE 218
e
f
We can use this or that to refer to something mentioned before.
I simply haven't got the money. This is/That's the problem.
Here this/that means 'the fact that I haven't got the money.' That is more usual.
Here are two examples from real conversations.
The rooms are so big. That's why it's cold.
Well, if you haven't got television, you can't watch it. ~ That's true.
But when we refer forward to what we are going to say, we use this.
What I'd like to say is this. The government has...
We can use that/those to replace a noun phrase with the and so avoid repeating
the noun.
The temperature of a snake is the same as that of the surrounding air.
(that= the temperature)
Those (people) who ordered lunch should go to the dining-room.
This can happen only when there is a phrase or clause after that/those, e.g. of the
surrounding air. That is rather formal in this pattern.