About the related concepts of carrier aggregation, which description are correct? (Multiple Choice)

About the related concepts of carrier aggregation, which description are correct? (Multiple Choice)
A . The primary cell is the cell in which the CA UE resides, that is, the PCell. The operation of the CA UE in this cell is no different from other R8/9 cells, only the PCell has the PUCCH channel.
B . A secondary cell refers to a cell that is configured to a CA UE by using RRC connection signaling, and operates on a secondary carrier to provide more radio resources for the CA U
C . SCell only has a down line and no uplink
D . Component carrier refers to the carrier corresponding to different cells participating in carrier aggregation
E . PCC anchor point, which refers to the high priority resident PCC selected by the eNodeB

Answer: ACD