Describe the languages generated by the regular expressions from the following list:

1. [abc]+ 2. [abc]* 3. [0-9]+ 4. [1-9][0-9]* 5. [a-zA-Z][a-zA-Z0-9_]* 6. (19|20)[0-9]{2}[- /.](0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])

6 is clearly a date, I just need to be positive on the first 5.