The correct answer is $\boxed{\text{B. Median}}$.
A symmetric distribution is a distribution that has the same shape on either side of the mean. The median is the value that divides the data set into two equal parts, with half of the values below the median and half of the values above the median. In a symmetric distribution, the median will always be equal to the mean.
If a perpendicular is drawn from the vertex to the base line of a symmetric distribution, the area on the right side of the perpendicular will always be greater than the area on the left side. This is because the mean is always located to the right of the median in a symmetric distribution.
Therefore, the median is the value that has the highest value in a symmetric distribution.
The mean is the average of all the values in the data set. It is calculated by adding up all the values and dividing by the number of values. The mean is not always located in the middle of the data set, and it can be affected by outliers.
The mode is the most frequent value in the data set. It is the value that occurs the most often. The mode is not always located in the middle of the data set, and it can be affected by outliers.
None of the above is not a correct answer.