**Core Concept**
The subarachnoid space is a component of the meningeal layers surrounding the brain and spinal cord, filled with cerebrospinal fluid (CSF). It plays a crucial role in protecting the central nervous system (CNS) from mechanical injury and maintaining homeostasis.

**Why the Correct Answer is Right**
The subarachnoid space ends at the level of the foramen magnum, which is the opening through which the spinal cord passes to enter the cranial cavity. This anatomical relationship is critical in understanding the pathophysiology of conditions such as Chiari malformations and syringomyelia. The arachnoid mater, a delicate membrane, covers the brain and spinal cord, forming the subarachnoid space, which contains CSF.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the subarachnoid space does not end at the level of the tentorium cerebelli, which is a separate meningeal structure separating the cerebrum from the cerebellum.
**Option B:** This option is incorrect because the subarachnoid space does not end at the level of the lamina cribrosa, which is a structure within the optic nerve head.
**Option C:** This option is incorrect because the subarachnoid space does not end at the level of the denticulate ligaments, which are fibrous structures supporting the spinal cord.

**Clinical Pearl / High-Yield Fact**
The subarachnoid space is a critical region for the administration of spinal anesthesia and epidural anesthesia, as it provides a direct route for local anesthetics to reach the spinal cord and block pain transmission.

**Correct Answer:** D.