Relative Pronouns

Firstly, watch this short video. (click on the video and then click where it says that want to wacth it on Youtube)

Now, read the following information:

Where refers to places.

Who refers to people.

Whom  (a quem) Click for more info

Which and that refer to objects or animals.

Whose is used to express possession.

When is used to refer to a time expression.

Why refers to a reason.

Now,  look at these examples!

e.g. For teenagers appearance is something which comes first. 
Over here, "which" refers to appearance.

The sentence above is defining relative clause. They are essential to the understanding of the context.

You can omit “who”, “that”, “which”, in defining relative clauses but only when they are the object. 

e.g. That’s the CD (which, that) my boyfriend gave me. 

In defining relative clauses when it’s an informal situation "that" can replace "who" or "which".

Defining relative clauses:

- Give information about who or what we are talking about;
- All the relatives can be used in defining clauses;
- You do not use commas.

Non-defining relative clauses:

- Give additional (extra) information about something;
- Normally it is added between commas;
- We can't omit who and which; 

Examples of non-defining relative clauses:

Whose 

e.g. John, whose girlfriend is Simone, has stopped smoking.

When we add extra information in a sentence, we put it between commas and call it non-defining relative clause.


Who

e.g. Tom, who is allergic to cats, is my neighbour. 

In this sentence, the important information is that Tom is her neighbour. The information that Tom is allergic is something the speaker wanted to share.


Have a look at these links:

http://www.englisch-hilfen.de/en/exercises/pronouns/relative_pronouns2.htm

http://www.ego4u.com/en/cram-up/grammar/relative-clauses (here you have an explanation about this and in the end of the page you have got links for more exercises.)