What does this sign mean?

a. When driving slow overtake to the right

b. Drive only in the right-hand lane

c. Keep in the right-hand lane when driving slow

The right-hand lane is for those who drive slowly.

Explanation:

a. It means that on the right-hand lane the traffic is slow. so if you want to travel at slower speed so you should use right-hand lane of the road.

b. Because right-hand lane is for those driver who want to travel at a slower speed.

c. Because on the other hand lane the traffic is fast, and if you drive slowly on the left-hand side so it may cause traffic accident. So that's why keep in the right-hand lane when you want driving slow.