(8pts) Write regular expressions for the following:

a.S = {a,b} L = { all words with one letter a in them}

b.S = {a,b} L = { all words that have two letter as or two letter bs in consecutive order }

c.S = {a,b,c} L = { where every b is immediately followed by a letter c }

d.S = {a,b,c} L = { all words with at least one substring of abc in them}