The correct answer is B. Light. Multi-mode cable refers to multi-mode fiber-optic cabling. In fiber-optic transmission, data is carried using light through the fiber core. HPE Aruba Networking's transceiver documentation explains that multimode fibers have thicker fiber cores and can transport light in multiple modes. The same HPE Aruba Networking transceiver guidance discusses optical transceivers transmitting light pulses and managing light loss across fiber-optic cabling. Therefore, in the context of multi-mode fiber, the signal being modulated to represent data is light. Option A is incorrect because radio is used in wireless transmission, not fiber-optic cabling. Option C is incorrect because voltage is associated with electrical copper cabling, such as twisted-pair Ethernet, rather than optical fiber. Option D is incorrect because pressure is not used as the signaling method for standard Ethernet fiber links. This question is focused on Layer 1 media behavior, and multi-mode fiber is a Physical Layer medium that transports optical signals between network transceivers.