C

Step 1: Analyze the velocity-time graph provided. The x-axis represents time in seconds, while the y-axis represents velocity in m/s.
Step 2: Identify the points on the graph. There is an initial increase in velocity from point A (10 s) to point B (120 s).
Step 3: Observing the graph, the fuel burns until the point where the velocity no longer increases (constant velocity after 120 s).
Step 4: Thus, the time of burning of fuel is from 0 s to 120 s.
Step 5: Therefore, the total burning time is 120 seconds.
Hence, the correct answer is C.