**Core Concept**
The spinal cord in adults terminates at a specific level due to the differential growth rates of the spinal cord and vertebral column. This anatomical characteristic is crucial for understanding various neurological conditions and surgical procedures.

**Why the Correct Answer is Right**
The spinal cord normally ends at the level of L1 (first lumbar vertebra) in adults. This is because the spinal cord grows at a faster rate than the vertebral column during fetal development. As a result, the spinal cord becomes relatively shorter compared to the vertebral column, leading to its termination at L1. This is an essential concept in neurosurgery and neurology, particularly when performing lumbar punctures or spinal surgeries.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the spinal cord does not typically end at the thoracic level in adults. The thoracic spine (T1-T12) is generally associated with the middle to upper back region.
**Option B:** This option is incorrect because the spinal cord does not typically end at the sacrum. The sacrum (S1-S5) is a fused set of vertebrae forming the base of the spine.
**Option C:** This option is incorrect because the spinal cord does not typically end at the coccyx. The coccyx, also known as the tailbone, is a small, triangular bone at the very bottom of the spine.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the spinal cord is generally 1-2 vertebral levels shorter than the lower border of the cranium (L1 level). This knowledge is crucial for performing lumbar punctures and avoiding spinal cord injury.

**Correct Answer: C. L1**