The assassination of archduke franz ferdinand might not have been a major international incident if (1 point) germany still had an alliance with russia britain had not signed a treaty with belgium luxembourg had resisted germany's invasion germany had invaded france directly

I believe the correct answer here is A,if Germany still had an alliance with Russia
This is because this is how the events progresseda. Austria Hungary was fired into war with Serbia for it was assured of Germany supportb.To attack Serbia, you would as well be declaring war on Russia,c. to attack Russia, you would be declaring war on France, which explains why Germany had to invade France as welld.To attack France and defeat it quickly,the easiest route was through Belgium, and attacking Belgium was attacking Great Britain because the two countries had a treaty.
The whole situation could thus have been avoided by  a Germany-Russian treaty.