Write regular expressions for the following languages: a) The set of all strings of O's and 1's not containing 101 as a substring. b) The set of all strings with an equal number of O's and 1's, such that no prefix has two more O's than 1's, nor two more 1's than 0's. c) The set of strings of 0's and 1's whose number of O's is divisible by five and whose number of 1's is even