From the CSSIA Kerberos Interactive, what does the Authentication Server $($AS$)$ maintain?

Question $2$ options:

a$)$

the keys generated by Bob and the TGS

b$)$

the keys generated by Bob

c$)$

the keys generated by Bob, the TGS$,$ and the application server

d$)$

the keys generated by the application server and the Ticket Granting Server $($TGS$)$