If a person travels a certain distance at a speed of 10 km/h, and returns through the same route at a speed of 20 km/h, then what will be the average speed during the whole journey?

A

$$\frac{40}{3}$$ km/h

B

15 km/h

C

$$\frac{10}{3}$$ km/h

D

$$\frac{20}{3}$$ km/h