Autofill in a control

I have a questionaire which houses a main form that
includes a respondant and one subform that houses a
respondant's answers to a series of questions. I have a
table with question code letters and the question
descriptions. Currently for Question A (for example) the
user needs to put in the question letter and then mark
their response to the question. Is there a way to make the
question letter autofill when the user goes to mark
his/her response. It seems no matter what I do, the
question letter area always comes up blank, needing to be
filled in? If anyone has advice, please let me know.

Thanks,
Lauren