That is the dress. I have paid for it.
That is the dress which/that I have paid for.
It's a can of lemonade. I bought it last month.
It's a can of lemonade which/that I bought last month.
She is the girl. I gave flowers to her.
She is the girl who/that I gave flowers.
It's a woman. Her dogs are lovely.
It's a woman whose dogs are lovely.
This is the woman. She teaches History at our school.
This is the woman who/that teaches History at our school.
Summer is my favourite time. I enjoy making sandcastles.
Summer is my favourite time when I enjoy making sandcastles.
That was the park. We hung out with my friends together there.
That was the park where we hung out with my friends together.
The library is my favourite place. I love looking for new books there and reading them.
The library is my favourite place where I love looking for new books there and reading them.
This is the reason. I hate reading science fiction.
This is the reason why I hate reading science fiction.
This is a dangerous burglar. The police have been running after him for several weeks.
This is a dangerous burglar who the police have been running after for several weeks.