A patient is scheduled to undergo a transtibial amputation of the left lower extremity. In addition the patient is one month post right total knee arthroplasty. Given the patient's past and current surgical history, the physical therapist assistant should expect which of the following activities to be the most difficult for the patient following their amputation?

A. Rolling from supine to sidelying
B. Moving from supine to sitting
C. Moving from sitting to standing
D. Ambulating in parallel bars