**Core Concept**
The spinal cord's dorsal and ventral roots are primarily responsible for transmitting and receiving nerve signals, respectively. This fundamental principle is essential for understanding the spinal cord's role in sensory and motor functions.

**Why the Correct Answer is Right**
Bell-Magendie's law states that the spinal cord's dorsal roots are sensory, while the ventral roots are motor. This distinction is critical for the proper functioning of the nervous system. The dorsal roots transmit sensory information from the periphery to the central nervous system, whereas the ventral roots transmit motor signals from the central nervous system to the periphery. This dichotomy is supported by the presence of sensory receptors in the dorsal root ganglia and motor neurons in the ventral roots.

**Why Each Wrong Option is Incorrect**
**Option A:** Laplace's law is a principle in physiology that describes the relationship between the pressure and radius of a blood vessel. It is not related to the spinal cord's dorsal and ventral roots.
**Option C:** Frank-Starling's law is a principle in cardiovascular physiology that describes the relationship between the stroke volume of the heart and the end-diastolic volume. It is not relevant to the spinal cord's dorsal and ventral roots.
**Option D:** Weber-Fechner's law is a principle in psychophysics that describes the relationship between the physical magnitude of a stimulus and the perceived magnitude of the stimulus. It is not related to the spinal cord's dorsal and ventral roots.

**Clinical Pearl / High-Yield Fact**
Bell-Magendie's law highlights the importance of understanding the distinct functions of the spinal cord's dorsal and ventral roots. This knowledge is critical for diagnosing and managing various neurological conditions, including spinal cord injuries and peripheral neuropathies.

**✓ Correct Answer: B. Bell-Magendie's law**