A 41-year-old patient presents to the clinic with left shoulder pain after a fall where he caught himself with his left arm. To assess the injury, the patient was asked to abduct both arms to 90 degrees and then to bring them anteriorly with a 30 degrees forward flexion. Then the patient was asked to move both thumbs downwards. The patient attempted to resist downward pressure and was unable to do so. This test assesses the integrity of the: A. Biceps tendon B. Deltoid muscle C. Infraspinatus muscle D. Supraspinatus muscle E. Teres minor muscle