Defining or Non-defining

I have three brothers.

• My brother who lives in Sidney came to see me last month.

• My brother, who lives in Sidney, came to see me last month.

Answer explanation

Because I have more than one brother, I have to define which brother I'm talking about.

I have one sister.

• My sister who is 25 years old spent her holiday in France.

• My sister, who is 25 years old, spent her holiday in France.

Answer explanation

As I have only one sister, It's not necessary to define who I am talking about.

Bob's mother has lost her keys.

• Bob's mother who is a musician has lost her car keys.

• Bob's mother, who is a musician, has lost her car keys.

Answer explanation

As usually, everybody has a mom, so it's not necessary to define.

My friend Jane moved to Canada.

• My friend Jane whose husband is Canadian moved to Canada last week.

• My friend Jane, whose husband is Canadian, moved to Canada last week.

Answer explanation

The person is identified, so it is not necessary to specify who I am talking about.

I am a shoe fanatic.

• The shoes which I bought yesterday are very comfortable.

• The shoes, which I bought yesterday, are very comfortable.

Answer explanation

Being a shoe fanatic means I have lots of them. So I have to define which shoes I am talking about.

Mr. Robinson is very famous.

• Mr Robinson whom I met at the trade fair is a famous inventor.

• Mr Robinson, whom I met at the trade fair, is a famous inventor.

Answer explanation

The person is identified by the name,so it's not necessary to define who I am talking about.

Tamara has two cats. Both of them are black.

• Tamara's two cats which can play outside are black.

• Tamara's two cats, which can play outside, are black.

Answer explanation

As she has only two cats, it's not necessary to define which cats I am talking about.

Kevin has four cats. Two of them are black.

• Kevin's two cats which are black can play outside.

• Kevin's two cats, which are black, can play outside.

Answer explanation

Kevin has four cats, I must define which of the cats I am talking about.

We are on holiday. Yesterday we visited a church.

• The church which we visited yesterday is very old.

• The church, which we visited yesterday, is very old.

Answer explanation

As it could be any chursch, I need to define which one Iam talking about.

We are on holiday. Yesterday we visited a church.

• St. Mary's Church which we visited yesterday is very old.

• St. Mary's Church, which we visited yesterday, is very old.

Answer explanation

The church is identified by its name, s it's not necessary to specify which oneIam talking about.