15. Consider the following regular expression: [az]+((-|_) [az]+){0,1}(\. [0-9]*)? Briefly explain why each of the strings from the following set that would or would not be matched by the above regex: (a) abc-X27 (b) abc_def. 27 (c) z. (d) abc-def_ghi345 (e) abc-def25.16