The correct answer is A. 10G-DAC. The limiting device in this connection is the CX 6200. HPE Aruba Networking CX 6200 models use built-in high-speed uplinks, and the CX 6200 product listings identify models with 4SFP+ uplinks. SFP+ uplinks support 10G, not 25G, 50G, or 100G single-port connectivity. HPE Aruba Networking transceiver guidance also notes that CX 6200 switches support split-side SFP connections only in available 10G-capable SFP ports, and that 50G transceivers can only be used in ports capable of 50G speeds, such as SFP56-capable ports. Therefore, even though the CX 8100 supports higher-speed connectivity options, the shared validated single-port option between the two switch families is 10G over DAC for a short 3-meter connection. Option B is incorrect because the CX 6200 does not have 100G ports. Option C is incorrect because 25G-LR is not the best validated 3-meter option and exceeds the CX 6200 SFP+ port capability. Option D is incorrect because 50G-DAC requires 50G-capable ports.