1. When Fred was young, he could understand, but he couldn't speak it.

2. He could play the guitar, but he couldn't sing.

3. He could swim really well, but he couldn't ride a bike.

4. Now, Fred can speak three languages fluently, but he can't play the guitar.

5. He can play the piano, but he can't drive a car.

When I was younger I could sleep for a long time. I couldn't speak English. Now, I can drive a car. I can't cook very well.