About the description of the gateway selection in EPC, which of the following are correct? (Multiple Choice)

About the description of the gateway selection in EPC, which of the following are correct? (Multiple Choice)
A . MME select S-GW according to the UE’s current TAI
B . In the process of Attach, select S-GW using the DNS parse function based on TAI
C . Should try to choose the P-GW unity with the selected S-GW
D . If UEA activates multiple PDN connections to a APN, these PDN connections can choose different PGW

Answer: ABC