An individual is being treated in an outpatient physical therapy clinic following a grade 2 ankle sprain. Four weeks have passed, and the patient has been gradually improving their strength and balance. The patient was able to perform single limb stance on the ground with their eyes closed for 30 seconds without pain or loss of balance (LOB). Which exercise would be the NEXT progression in difficulty?

a) single limb stance on a balance board
b) modified tandem on an airex pad
c) tandem stance on an airex pad
d) single limb stance with eyes closed on a balance board