Based on the output,
vyatta@VYA1:~$ show ip ospf database
OSPF Router with ID (172.24.42.51) (Process ID 0)
Router Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum Link count
172.24.42.51 172.24.42.51 167 0x80000008 0xa98e 3
172.24.42.52 172.24.42.52 166 0x80000006 0x21e7 3
172.24.42.53 172.24.42.53 6 0x8000000b 0x7854 3
172.24.42.54 172.24.42.54 7 0x80000003 0x1183 4
Net Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# CkSum
192.168.12.1 172.24.42.51 327 0x80000002 0x92e8
192.168.13.3 172.24.42.53 32 0x80000002 0x6d08
192.168.23.3 172.24.42.53 602 0x80000002 0x0d5d

192.168.160.3 172.24.42.53 10 0x80000003 0x3e9f
AS External Link States
Link ID ADV Router Age Seq# CkSum Route Tag
0.0.0.0 172.24.42.51 187 0x80000003 0x04a1 E2 0.0.0.0/0 254
which router is advertising the default route?

A.
172.24.42.51

B.
172.24.42.52

C.
172.24.42.53

D.
172.24.42.54