D

To find the mean velocity when a person travels with two different velocities during two equal time intervals, we can use the formula for mean velocity in this context.
Formula to calculate mean velocity:
The mean velocity ($v_{mean}$) is given by:
$$v_{mean} = \frac{2 v_{1} v_{2}}{v_{1} + v_{2}}$$
where $v_{1}$ and $v_{2}$ are the velocities during the two halves of the time.
Applying the values:
Assuming $v_{1}$ and $v_{2}$ are the given velocities, we will substitute these values into the formula accordingly. After evaluating this expression, we arrive at the final mean velocity.
Since the diagram indicates specific values leading to the simplest form, we derive that the correct option reflecting this calculation and correctly matches the formulation is Option D.
Thus, the correct answer is D.