Restrictive and non-restrictive clauses

[Bassim]

Please, would you correct my mistakes in these sentences. My main problem is that I often do not know if the second part of a sentence is restrictive or non-restrictive. For example:

1. Today I talked to Peter who had been working in our company for many years.
2. John is a friend of mine who tried to find a proper job but never succeeded.
3.The woman showed me a book which she received as a present for her birthday.

 

[5jj]

1. Today I talked to Peter who had been working in our company for many years.
Here, the person you talked to has been defined by his name. The information about how long he has been working for the company is therefore non-defining. You need a comma,

2. John is a friend of mine who tried to find a proper job but never succeeded.
Here, only the speaker knows whether the information about finding a proper job is defining or not. If it is not, the sentence (which would need a comma) is not very natural, but it's just about possible. If you wanted to give this meaning, it would be far more natural as "John, who is a friend of mine, tried to find a proper job but never succeeded". If I had to punctuate the original in an examination, I'd assume it was a defining clause - no comma.

3.The woman showed me a book which she received as a present for her birthday.
This could be defining or, with a comma, non-defining.