At the shallow end of a swimming pool, the water is 70.0 cm deep. The diameter of the cone of light emerging from the water into the air above, emitted by a light source 10.0 cm in diameter at the bottom of the pool and measured by an observer on the edge of the pool 2.50 m away, is
(a) 1.60 m.
(b) 1.70 m.
(c) 1.75 m.
(d) 1.80 m.