Create the same parameter in both main and subreports. Then in the in subreport linking screen, move {?question} to the right (from the main report), and in the bottom left corner, use the dropdown to select {?question}, NOT the default {?pm-?question}.
In both the main and in the subreport, go to report->selection formula and make sure it says:
{table.question} = {?question}
Do not link on any other fields. Make sure you are sorting both main and subreports the same way so that the answers will correspond to the questions.
-LB