**Core Concept**
Hemorrhagic shock is a condition characterized by reduced blood volume leading to inadequate tissue perfusion. It is classified into four classes based on the percentage of blood loss: Class I (15-30% blood loss), Class II (30-40% blood loss), Class III (40-50% blood loss), and Class IV (more than 50% blood loss).

**Why the Correct Answer is Right**
Class I hemorrhagic shock occurs when there is a blood loss of 15-30%. This class is often referred to as the "compensated" stage of hemorrhagic shock, where the body is still able to maintain adequate blood pressure and tissue perfusion through compensatory mechanisms such as vasoconstriction and tachycardia. The body's compensatory mechanisms can maintain blood pressure and tissue perfusion until the blood loss reaches 30%.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct percentage of blood loss for Class I hemorrhagic shock.
**Option B:** This option is incorrect because it is not a valid classification of hemorrhagic shock.
**Option C:** This option is incorrect because it specifies a higher percentage of blood loss, which corresponds to Class II hemorrhagic shock.
**Option D:** This option is incorrect because it specifies an even higher percentage of blood loss, which corresponds to Class III hemorrhagic shock.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the classification of hemorrhagic shock is based on the percentage of blood loss, and each class has distinct clinical features and management strategies.

**Correct Answer: C. 40-50% blood loss.**