(A) Italy
(B) Yugoslavia
(C) Turkey
(D) ** Bulgaria
EXPLANATIONS BELOW
Concept note-1: -The Incident at Petrich, or War of the Stray Dog, was a Greek–Bulgarian crisis in 1925 that resulted in a brief invasion of Bulgaria by Greece near the border town of Petrich after the killing of a Greek captain and a sentry by Bulgarian soldiers.
Concept note-2: -The Second Balkan War was a conflict which broke out when Bulgaria, dissatisfied with its share of the spoils of the First Balkan War, attacked its former allies, Serbia and Greece, on 16 (O.S.) / 29 (N.S.) June 1913. Serbian and Greek armies repulsed the Bulgarian offensive and counter-attacked, entering Bulgaria.
Concept note-3: -At 475 km in length, the border between Bulgaria and Greece begins in the west at the tripoint between the borders of Bulgaria, Greece and Macedonia.