Make one sentence from each pair of sentences using a relative clause

1. I don't know the woman. Her son is waving at me

I don't know the woman.........................is waving at me

2. 12th December is a very special date for us. We got married that day

12th December is the day..............................got married

3. These dresses are made by hand. That's why they're so expensive

The  reason..................................is that they are made by hand