Checkbox instead of listbox on subform

[lsmcal1984]

I am creating a database that logs responses to questions and each contact can answer any number of questions.
I have created a contact, questions and LinktoQuestion table, where all responses are logged.
I loaded a continuous subform into the contact form and I was presented with the option to select questions from a list box.
At the moment, the subform is bound to the Questions Table. If I try to bound to the LinkToQuestion table, it will not allow me to add/edit records.
I wish the subform to display all available questions and then the user selects the questions answered (as shown – but not working).
Database attached.

Thanks for your help guys.