To find the average speed of the car, we need to calculate the total distance traveled and divide it by the total time taken. Let's analyze the given graph.

The graph shows the speed of the car over different time intervals. We will calculate the distance covered in each segment and sum them up to find the total distance.

1. From 0 to 1 hour, speed = 10 km/h. Distance = \(10 \times 1 = 10\) km.
2. From 1 to 3 hours, speed = 30 km/h. Distance = \(30 \times 2 = 60\) km.
3. From 3 to 4 hours, speed = 40 km/h. Distance = \(40 \times 1 = 40\) km.
4. From 4 to 5 hours, speed = 30 km/h. Distance = \(30 \times 1 = 30\) km.
5. From 5 to 7 hours, speed = 0 km/h. Distance = \(0 \times 2 = 0\) km (no movement).

Total distance = 10 + 60 + 40 + 30 + 0 = 140 km.

Total time taken = 7 hours.

The average speed is given by the formula:

\(\text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}} = \frac{140}{7} = 20\) km/h.

Based on the given options, the closest value is 21.43 km/h, which seems to be an approximate answer due to possible interpretation errors from the graph or approximations.

Therefore, the average speed of the car is approximately 21.43 km/h.