Generate a question which can yield the answer mentioned in the input. Generated question must be answered by the answer provided in input, without using any extra knowledge.
Q: Context : The Salonika Agreement (also called the Thessaloniki Accord) was a treaty signed on 31 July 1938 between Bulgaria on the one hand and the Balkan Entente--the states of Greece, Romania, Turkey and Yugoslavia--on the other.
Answer : 31 July 1938
A:
What is the date when Salonika Agreement happened?