A photograph of a landscape is captured by a drone camera at a height of 18 km . The size of the camera film is $$ 2 cm \times 2 cm $$ and the area of the landscape photographed is $$ 400 km^{2} $$. The focal length of the lens in the drone camera is :

A

1.8 cm

B

0.9 cm

C

2.8 cm

D

2.5 cm