RegEx / computer theory - construct a regEx in alphabetical order

Question

In my grammars - Computer theory class I am trying to create a regular expression in alphabetical order(a-z)

l = {a, b, x, y, z, i, o, u, e, c}

<

Answer 1

the word must be in alphabetical order, so if it contains any a's, they surely must be at the front. likewise, if it contains any b's , they must come after the a's, and nothing can come in between the a's and b's

so we have: a*b*...

and so a pattern emerges.