The plot below shows the relationship between the mortality risk of cardiovascular disease and the number of steps a person walks per day. Based on the data, which one of the following options is true?
- The risk reduction on increasing the steps/day from $0$ to $10000$ is less than the risk reduction on increasing the steps/day from $10000$ to $20000$.
- The risk reduction on increasing the steps/day from $0$ to $5000$ is less than the risk reduction on increasing the steps/day from $15000$ to $20000$.
- For any $5000$ increment in steps/day the largest risk reduction occurs on going from $0$ to $5000$.
- For any $5000$ increment in steps/day the largest risk reduction occurs on going from $15000$ to $20000$.