PC establish l2tp vpn through the vpn client and USG (LNS), what are possible reasons of dial-up failure?

One network is shown as below:

PC establish l2tp vpn through the vpn client and USG (LNS), what are possible reasons of dial-up failure? (Select 3 Answers)
A . The tunnel name of the LNS is not consistent with the client’s.
B . L2TP tunnel authentication failed.
C . PPP authentication fails, the PPP authentication mode set on the client PC and LNS is not consistent.
D . The client PC can not obtain the IP address assigned to it from the LN

Answer: BCD