Question

What old books has been referred to here?
lesson 1 the Fun they had
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Answer 1

Explanation:

They' refer to the people of the old times. Here, regular refers to the mechanical teacher then they had. It is contrasted with a normal teacher of earlier times, who was a living human being.

...

The pages of the book were yellow because the book was quite old.

Yes, Margie saw the book for the first time.

Crinkly.

Answer 2

                                   THE FUN THEY HAD

                                                       - Isaac Asimov

In this story isaac asimov imagines and writes about the future world

in where the old book is mentioned as old and made of pages by tommy and margie  also the book was compared with their period learning gadgets