Step 1: Repeater Guideline. For Ethernet (10Base-T/100Base-T), the standard maximum cable length before a repeater is necessary is generally 100 meters. Step 2: Distance Verification. - A to B = 20m → Below 100m → Repeater not required. - A to C = 50m → Below 100m → Repeater not required. - A to D = 110m → Exceeds 100m → Repeater is mandatory. - A to E = 70m → Below 100m → Repeater not required.
Conclusion: \[\boxed{\text{Connection from A to D}}\]