Fill in since, for or ago.
Remember: You use ago only in connection with PAST TENSE because the action took place in the past.
since and for are used in connection with PRESENT PERFECT because the action itself or the result is still visible.

1. She used to sing in a choir ten years .
2. Frank and Charles have played baseball many year.
3. They have played tennis 1999.
4. Dan studied English twenty years , but he hasn't spoken this language at least five years.
5. New Year's Eve she hasn't smoked any cigarette.