Adjective Clauses
Adjective clauses (or relative clauses) are a type of subordinate clause that act as adjectives. The whole clause does the job of an adjective. I'll show you what I mean with some examples below.

Quick Refresher: Adjectives modify nouns and pronouns. Clauses are groups of words with a subject and a verb, and subordinate clauses cannot stand alone.

Examples

Mr. Clean, who hates rock music, smashed my electric guitar.
Mr. Clean smashed my electric guitar, which had been a gift from Vera.
Mr. Clean smashed the electric guitar that Vera had given me.This clause is an adjective clause. It is a group of words with a subject and a verb, and it is acting as one part of speech - an adjective.

Now the adjective clause is just the words I love, but the word that is implied. It's as if the sentence says:

The instrument (that) I love is the piano.

Whenever words are implied in a sentence, it is called an elliptical.

The technical name for a missing relative pronoun is an elliptical relative pronoun.

If you want to diagram the sentence, diagram the implied relative pronoun in parenthesis.



Relative Adverbs

While most of the time relative clauses are introduced by relative pronouns, sometimes they are introduced by relative adverbs (where, when, why, before, since).

Here are some examples. Notice that the clause is still modifying a noun.

    This is the park where we played.

    Tuesday is the day when we have pizza for dinner.

    Our teacher told us the reason why we study grammar.


 Example a part of article containing the adjective clause (underline) :

         Germans typically have very few friends, however friendships that do develop typically last a lifetime, as loyalty is held in high regard. Friends in Germany are expected to help each other in every possible sense. Germans may appear aloof to people from other countries, as they tend to be cautious and keep their distance when it comes to meeting new people, which explains ongoing intercultural differences with people from English-speaking countries. The development from becoming an acquaintance to a friend can take several months.
         Americans are known for being very friendly, however, it is often the case that Americans are quick to form friendships, but the friendships do not necessarily last. Americans also use the term “friend” very freely. They refer to someone they have known for a few weeks as a friend, perhaps because there is not a term for someone who is more than an acquaintance but less than a friend. It is also common for Americans to turn to outsiders such as therapists for help in situations where people from other cultures would turn to friends. Americans are known for valuing independence. Americans are also very self driven and hard working. As a result of these characteristics, some Americans who had a tendency to become so wrapped up in their work that they either forget about their friends or have no time to spend with them. Perhaps our pride driven nation which is one reason for the decline in friendship in the U.S (Copeland, 2001).

Questions and Answers of the excercises :
Q 1. I talked to the woman she was sitting next to me
A 1. I talked to the woman who was sitting next to me

Q 2. I have a class it begins at 08.00 Am
A 2. I have a class which begins at 08.00 Am

Q 3. The man called the police his car was stolen
A 3. The man whose car was stolen called the police

Q 4. The building is very old he lives there
A 4. The building where he lives is very old

Q 5. The woman was ms Silvy I saw her
A 5. The woman whom I saw was ms Silvy


Reference :   
http://faculty.deanza.edu/flemingjohn/stories/storyReader$20
http://www.chompchomp.com/terms/adjectiveclause.htm
http://www.englishclub.com/grammar/pronouns-relative.htm
http://eslbee.com/AdjClauses.htm