Step 1: The slope of the velocity-time graph represents the acceleration of the body. In this case, the graph is a straight line making an angle of \( 60^\circ \) with the time axis. The slope of the line is given by:
\[
\text{Slope} = \tan(\theta)
\]
where \( \theta = 60^\circ \).
Step 2: The value of \( \tan(60^\circ) \) is known to be \( \sqrt{3} \). Therefore, the acceleration of the body is:
\[
\text{Acceleration} = \tan(60^\circ) = \sqrt{3}
\]
Step 3: Hence, the body is moving with an acceleration of \( \sqrt{3} \) m/s\( ^2 \). Therefore, the correct answer is option (D).