**Core Concept**
The Rule of Hasse is a mathematical formula used in forensic anthropology to estimate the fetal age of an unborn child based on the length of the long bones. This calculation is essential in determining the gestational age, which can be crucial in various forensic and medical investigations.

**Why the Correct Answer is Right**
The Rule of Hasse takes into account the length of the long bones, particularly the femur, humerus, and tibia, to estimate the fetal age. This method relies on the principle that the length of the long bones increases in a predictable manner as the fetus develops. The formula accounts for the growth rate of the bones and the average length at different gestational ages. By applying this formula, forensic experts can estimate the age of the fetus with a reasonable degree of accuracy.

**Why Each Wrong Option is Incorrect**
**Option B:** The height of an adult is determined using different formulas, such as the Rohrer's formula or the Haycock's formula, which take into account various body measurements, not just the length of long bones.
**Option C:** Race is not determined by the Rule of Hasse, as this formula is based on the measurement of fetal bones, which do not provide sufficient information to identify an individual's racial background.
**Option D:** Identification is a broader concept that involves matching an unknown individual with a known person or set of characteristics. The Rule of Hasse is a specific tool used in forensic anthropology to estimate fetal age, not for identification purposes.

**Clinical Pearl / High-Yield Fact**
In forensic medicine, estimating fetal age is crucial in cases of stillbirth, fetal demise, or suspected fetal abuse. The Rule of Hasse is a valuable tool in these situations, but it is essential to consider other factors, such as the mother's medical history and any potential teratogenic exposures, to arrive at an accurate estimation of fetal age.

**✓ Correct Answer: A. Age of fetus**