【单选题】

The nurse is administering warfarin (Coumadin) to a client with deep vein thrombophlebitis. Which laboratory value indicates warfarin is at therapeutic levels
A．Partial thromboplastin time (PTT)

to 2 times the control.
B．Prothrombin time (PT)
to 2 times the control.
C．International normalized ratio (INR) of 3 to 4.
D．Hematocrit of 32%.