**Core Concept**
The question is testing the student's understanding of the SI unit of radiation dose, specifically the Gray (Gy) and its relation to the Sievert (Sv). The Gray is a measure of absorbed radiation dose, while the Sievert is a measure of the biological effect of radiation.

**Why the Correct Answer is Right**
The Sievert (Sv) is a unit of dose equivalent, which takes into account the relative biological effectiveness (RBE) of different types of radiation. One Sievert is equivalent to one Gray for gamma radiation, but for alpha particles, it is 20 times higher due to their higher RBE. The correct answer is the option that reflects this relationship.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely incorrect because it doesn't take into account the RBE of different types of radiation.
**Option B:** This option might be incorrect because it doesn't specify the type of radiation used to define the Sievert.
**Option C:** This option is likely incorrect because it doesn't accurately reflect the relationship between Gray and Sievert.

**Clinical Pearl / High-Yield Fact**
Remember that the Sievert is a measure of the biological effect of radiation, and it's essential to consider the RBE of different types of radiation when assessing radiation dose.

**Correct Answer: C. 5 rems**