Join the sentences with so It was my sister's birthday. We bought her a phone. It was my sister's birthday, so we bought her a phone 2 The phone didn't work. We decided to change it. 3 My dad showed the receipt. My sister got her new phone, 4 My parents couldn't find their wallets. They couldn't pay for lunch.

**Решение:** 1. It was my sister's birthday. We bought her a phone. - **Combined using "so":** It was my sister's birthday, so we bought her a phone. 2. The phone didn't work. We decided to change it. - **Combined using "so":** The phone didn't work, so we decided to change it. 3. My dad showed the receipt. My sister got her new phone. - **Combined using "so":** My dad showed the receipt, so my sister got her new phone. 4. My parents couldn't find their wallets. They couldn't pay for lunch. - **Combined using "so":** My parents couldn't find their wallets, so they couldn't pay for lunch. These sentences have been successfully combined using "so" to show the logical connection between the events or actions described in each pair of sentences.