根据句意及首字母提示完成句子。
1. —Did your sister use to have straight hair?
    —No, she used to have c_________ hair.
2. Mr. Green is really s _________, for he never smiles.
3. Amy used to be quiet, but now she is very o_________.
4. —Did you u ________ to play the piano?
    —Yes. I used to play the guitar, too.