**Core Concept**
Blood storage at 4°C is a common practice for preserving red blood cells, but it has limitations. This process involves refrigerating blood to slow down the metabolic processes of red blood cells, thereby prolonging their viability. The storage duration is critical for ensuring the safety and efficacy of blood transfusions.

**Why the Correct Answer is Right**
When blood is stored at 4°C, the metabolic rate of red blood cells decreases, reducing the accumulation of waste products like lactate and ammonia. This helps maintain the viability of red blood cells for a longer period. Typically, blood can be stored for up to 35 days at 4°C, but the exact duration may vary depending on factors like the storage medium and the condition of the blood.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because there is no standard storage duration mentioned in medical literature for blood stored at 4°C. The actual duration can vary based on several factors.

**Option B:** This option is incorrect because blood stored at room temperature (20-24°C) typically has a shorter shelf life compared to blood stored at 4°C.

**Option C:** This option is incorrect because blood stored at -80°C is not a common practice for preserving red blood cells. This temperature is more suitable for freezing plasma or other blood components.

**Clinical Pearl / High-Yield Fact**
It is essential to follow strict protocols for blood storage, handling, and transfusion to prevent adverse reactions and ensure patient safety.

**Correct Answer: C. 35 days.**