The x-t graph shown in the question represents the position-time relationship of a body. It shows how the position of the body changes with respect to time.

Option 1: Positive acceleration - Positive acceleration means that the velocity of the body is increasing. However, from the graph, we can see that the slope of the line is not increasing over time. Therefore, option 1 is not depicted by the graph.

Option 2: Negative acceleration - Negative acceleration means that the velocity of the body is decreasing. The graph shows a constant, negative slope, indicating that the velocity is decreasing over time. Therefore, option 2 is depicted by the graph.

Option 3: Zero acceleration - Zero acceleration means that the velocity of the body is not changing. The graph shows a straight line with a constant slope, indicating that the velocity is not changing over time. Therefore, option 3 is depicted by the graph.

Option 4: None of these - Since option 3 is depicted by the graph, option 4 is not correct.

Therefore, option 3 (Zero acceleration) is the correct answer.