Use could or couldn " t to complete each sentence

ll .  Use could or couldn " t to complete each sentence.
1.  When l was young, l .............. play the guitar. lt was too difficult for me .
2. Her grandmother was bilingual. She ............ speak both Einglish and Spanish.
3. Yesterday, peter.............. do that exercise alone . So, he called me for help.
4. ln 1950, people ................use mobile phones.
5. When his mother was young, she ............ skate but she can" t do it any longer.