**Core Concept**
The amount of blood loss during each menstrual period is a critical aspect of female reproductive health. Menstrual blood loss is a complex process involving the hormonal changes, uterine contractions, and the shedding of the endometrial lining. The average menstrual blood loss is approximately 30-40 milliliters (mL) per period.

**Why the Correct Answer is Right**
The correct answer reflects the average menstrual blood loss, which is a result of the hormonal changes, particularly the decrease in progesterone levels, leading to the relaxation of the uterine smooth muscle. This relaxation causes the endometrial lining to detach and shed, resulting in menstrual bleeding. The average menstrual blood loss is about 30-40 mL, which is a normal physiological process.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it significantly underestimates the average menstrual blood loss. Menstrual blood loss can vary from person to person, but 10 mL is too low to be considered a normal average.
**Option B:** This option is incorrect because it overestimates the average menstrual blood loss. While some women may experience heavier menstrual bleeding, 100 mL is not a typical average for most women.
**Option C:** This option is incorrect because it is a range rather than a specific value. While menstrual blood loss can vary, providing a range does not accurately reflect the average amount of blood loss.

**Clinical Pearl / High-Yield Fact**
It's essential to note that menorrhagia, or heavy menstrual bleeding, is defined as blood loss exceeding 80 mL per period. This condition can lead to significant morbidity and impact a woman's quality of life.

**Correct Answer:** C. 30-40 mL.