CS2121 lab exercise 1 part a7 - hint

Just as in part a4, you need to match all the characters on the line - otherwise, you might let a lower-case letter slip through! However, for this part, you are not just looking for lines containing a single character, so you must allow for more than one character on the line.
Try thinking about the problem again. Start by thinking about what you want to achieve and how you might go about achieving it, even if you don't know exactly how to write it down.

If you are still stuck, here are some more hints.