A rain drop starts falling from a height of 1 km. It falls with a continuously decreasing acceleration and attains its constant terminal speed after falling through a height of 500 m. Then, the work done by the gravitational force in the first half and the second half of the drop's journey are in the ratio
(a) 1 : 1 and the times of fall of the drop in the two halves are in the ratio n:1 (where n >1)
(b) 1 : 1 and the times of fall of the drop in the two halves are in the ratio n :1 (where n <1)
(c) n : 1 (where n >1) and the times of fall of the drop in the two halves are in the ratio 1 : 1
(d) n : 1 (where n < 1) and the times of fall of the drop in the two halves are in the ratio 1 : 1