Deltoid is innervated by axillary nerve, which comes from roots C5/C6. Actions of the deltoid include abduction of the upper extremity.
question #15553 in UW explains this one well. Basically, C5 branches innervate Deltoid (abduction) and Infraspinatus(external rotation) and C6 Biceps (forearm flexion), so the right option should be abduction of the upper extremity.
I got it wrong though lol