C = {a,e,i,o,u} D = The set containing all the lowercase letters in the English alphabet

Let Q5 = the set of all strings over the alphabet C that contain just es Is Q5 a regular language over the alphabet D? Explain how you know

Find a regular expression to describe: The set of all strings over the alphabet {a, b, c, d} that contain exactly one a and exactly one b So, for example, the following strings are in this language: ab, ba, cccbad, acbd, cabddddd, ddbdddacccc and the following strings are NOT in this language: a, ccbc, acbcaaacba, acacac, bcbbbbbca, aca, c, d, b

Find a regular expression to describe L, where L = The set of strings over the alphabet {a, b, c, d} where every c is immediately preceded and also followed by a b (i.e. every c has the symbol b right next to it on both sides) So, for example These strings are in L: a, b, d, bcb, abbbbcbddabcb, abd, dbcbcb, bcbcb and these strings are NOT in L: abc, abcbabc, asdc, cbbb, acb