Which postulate or theorem can be used to prove that AABC = ADCB?
SSS
ASA
SAS
AAS

SSS congruency criteria can be used here to prove ∆ABC ≅ ∆DCB
In ∆ABC and ∆DCB
AB = CD (given)
AC = BD (given)
BC = BC (common)
So, by SSS congruency criteria,
∆ABC ≅ ∆DCB