**Core Concept**
Blood storage at 4°C is a critical aspect of transfusion medicine, as it affects the viability and function of red blood cells (RBCs). The storage of blood at this temperature slows down the metabolic processes, thereby reducing the rate of RBC degradation.

**Why the Correct Answer is Right**
The correct answer is related to the concept of RBC storage duration. Blood can be stored for 21-35 days at 2-6°C, with the optimal storage temperature being 2-4°C. The storage duration is influenced by the type of anticoagulant used, the storage container, and the presence of preservatives. The most commonly used anticoagulant is CPD (citrate-phosphate-dextrose), which helps to maintain RBC viability by reducing hemolysis and preserving ATP levels. During storage, RBCs undergo changes, including a decrease in 2,3-Bisphosphoglycerate (2,3-BPG) levels, which affects their ability to release oxygen to tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the optimal storage temperature and duration. Blood stored at 4°C can be kept for a longer duration than what is stated in this option.
**Option B:** This option is incorrect because it is too short a duration for blood storage at 4°C. Blood can be stored for several weeks at this temperature.
**Option C:** This option is incorrect because it is too long a duration for blood storage at 4°C. While blood can be stored for several weeks, the exact duration depends on various factors, including the storage conditions.

**Clinical Pearl / High-Yield Fact**
A key aspect of blood storage is the use of preservatives to maintain RBC viability. The most commonly used preservative is citrate-phosphate-dextrose (CPD), which helps to reduce hemolysis and preserve ATP levels in RBCs.

**Correct Answer:** C.