Step 1: Concept
Analyze the starting point and slope of the velocity-time graph.
Step 2: Meaning
The graph starts at a high value on the v-axis and decreases to zero.
Step 3: Analysis
At $t=0$, the velocity value is at its highest point on the graph.
Step 4: Conclusion
The body has maximum velocity at $t=0$.
Final Answer: (D)