**Core Concept**
Glucose concentration in cerebrospinal fluid (CSF) is lower than in blood plasma due to the blood-brain barrier's limited permeability to glucose. This difference is essential for maintaining the proper environment within the central nervous system (CNS).

**Why the Correct Answer is Right**
The glucose concentration in CSF is approximately 60-70% of that in blood plasma, mainly due to the limited glucose transport across the blood-brain barrier by glucose transporter 1 (GLUT1). This selective permeability ensures that glucose is available to the neurons while maintaining a stable environment. Additionally, the glucose concentration in CSF is also influenced by the rate of glucose consumption by neurons, which is higher than in other tissues.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided.
* **Option B:** This option is not provided.
* **Option C:** This option is not provided.
* **Option D:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
A notable exception to the general rule of lower glucose concentration in CSF is during conditions of increased glucose consumption, such as in bacterial meningitis or other CNS infections. In these cases, the glucose concentration in CSF can be significantly lower than in blood plasma.

**Correct Answer:** None of the above (since options A, B, C, and D are not provided).