If not, try looking here again.

If you are sure, then the only other thing I can think of is that you might need to use "( )" brackets to protect your original patterns when you combine them - I didn't need to, but maybe your answers to the earlier parts are different.

For example, just as in arithmetic expressions, the following regular expressions have completely different meanings:

(a+b)*(c+d)and:

a+(b*c)+dbut, for regular expressions, neither of the above is the same as:

a+b*c+dFor example, even though all three can match "abcd", only the first can match "cd", and only the second can match "abcbcd".