74 years old female complaining of pain and stiffness in the hip and shoulder girdle muscles. She is also experiencing low grade fever and has depression

74 years old female complaining of pain and stiffness in the hip and shoulder girdle muscles. She is also experiencing low grade fever and has depression. On examination no muscle weakness detected (Polymyalgia rheumatic). Investigation of choice:
a) RF
b) Muscle CK
c) ESR.