1. ( 3 points) Given the following regular expression, describe the set of strings it defines. Generalize as much as possible; i.e., don't just read back the regular expression to me. nzd dig* ed ed where nzd =1239, dig = nzd 0, and ed =02468 2. (3 points) Describe the following set using a regular expression: the set of strings that contain exactly 3 a's, over the alphabet ={a,b,c}. 3. ( 2 points) An extension to regular expressions is the use of the ' + ' symbol. Convert the following regular expression to use the ' + ' symbol: (1+) digit digit*