a) Define pattern matching techniques
b) Define subpatterns within the complete pattern
c) Define portion of strings in the regular expression
d) matching the complete string

Answer: b
Explanation: When a regular expression is successfully matched against a target string, it is possible to extract the portions of the target string that matched any particular paranthesized subpattern. The essential purpose of parantheses in regular expressions is to define subpatterns within the complete pattern.