**Core Concept:** Normal distribution curve, also known as Gaussian distribution, is a statistical concept representing the distribution of data points around a mean value. It is commonly described by its mean, median, and mode.

**Why the Correct Answer is Right:** In a normal distribution curve, the true statement is that the mean, median, and mode are all equal. This implies that the distribution is symmetrical and the middle values are identical. The correct answer is: March 2011 (mean) = March 2013 (median) = March 2011 (mode)

**Why Each Wrong Option is Incorrect:**
A. The statement is not true for the mean being equal to March 2013 as in a normal distribution, the mean is not fixed and can vary based on the data points.
B. Similarly, March 2013 is not the median, as the median is the middle value(s) in the distribution and cannot be a specific date.
C. Although the mode is the most frequently occurring value in a normal distribution, it is not equal to March 2011, as the mode can be different from the mean or median.

**Why Option D is Right:** March 2011 is the mode since it is the most frequently occurring value in the distribution, making all three values (mean, median, and mode) equal to March 2011.

**Clinical Pearl:** Understanding normal distribution and its characteristics is essential for analyzing and interpreting data in medical research, statistics, and clinical practice. It helps determine the center, spread, and shape of the data distribution, which are vital for drawing conclusions and making decisions based on the data collected.