The maximum efficiency of a screw jack is

(a) \(\frac{1-\sin \phi}{1+\sin \phi}\)

(b) \(\frac{1+\sin \phi}{1-\sin \phi}\)

(c) \(\frac{1-\cos \phi}{1+\cos \phi}\)

(d) \(\frac{1-\sin \phi}{1+\cos \phi}\)