Ganga and Saraswati, working separately can mow a fleld in 8 and 12 hours respectively. If they work in stretches of one hour alternately, Ganga beginning at 9 a.m., when will the moving be completed ?

Options

A. 6 p.m.
B. 6.30 p.m.
C. 5 p.m.
D. 5.30 p.m.