At the close of world war i, three countries were considered the "big three" for diplomatic purposes. who were they
russia
united states
germany
france
china
great britain

The big three for diplomatic purposes were
1) United States
2) Great Britain
3) France

Why it is not these:
Russia was not part of the big 3 during ww1 because they dropped out of the war early on... so it is not correct. 
Germany was on the losing side... so obviously it is incorrect
China did not play as significant of a role as most other countries, so it is incorrect. 

hope this helps

Where’s the diagrams?