Answer is B
Area of pond in map = 100 cm2 => Length of the pond in map = 10cm
Actual area of the pond = 10000 m2 => Actural length of the pond = 100m or 10000cm
So the ratio is given by
=> Length of the pond in map / Actual length in relief
=> 10/10000
=> 1/1000 or 1:1000