Question: What type of link is used between a mobile base station relay and served UEs, as well as between the mobile base station relay and the donor NG-RAN?
Option 1: PC5-based link
Option 2: NR-Uu link
Option 3: IAB-based link
Option 4: LTE-Uu link
Explanation: According to the text, the radio link used between a mobile base station relay and served UEs, as well as between the mobile base station relay and the donor NG-RAN, is assumed to be NR-Uu. This indicates that the correct answer is Option 2, which specifies an NR-Uu link.