A question about 'the'

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Jul 20, 2011 20:04 English grammar
Hi, it's been a long time.
I'm studying English with a textbook titled 'Common mistekes at IELTS Advanced'.
http://www.amazon.co.uk/Common-Mistakes-IELTS-Advanced-Avoid/dp/0521692474

I can't understand the explanation of the chapter of 'the before general concepts'.

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[explanation]
We use 'the' before nouns which describe a general type of thing rather than a specific example of that thing:

[examples]
1.
These are problems for students living away from 'the family'.
2.
We don't know the effects of such chemicals on 'the body'.
3.
The role of 'the student' at university level varies greatly from country to country.
4.
Most of our business is carried out over 'the telephone'.

*I used single quotes instead of bold words in the textbook

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I can't catch what the explanation really intend to say.
I also don't know why we should put 'the' for example 2 and 4.

I would like to ask you a favor of helping me.

P.S.
I will be in the UK from the 27th in July to see the graduate schools for about a week!