During world war i, developments in military
technology led to
(1) an early victory by the allied powers
(2) the establishment of industrial capitalism
(3) the use of poisonous gas and submarine
attacks
(4) an increase in ethnic tension in western
europe

The correct answer in short is (3) the use of poisonous gas and submarine attacks. 

During the World War I, many technological, medical and military advances happened.

Developments in military technology especially were ones to be frightful of. These developments led to (3) the use of poisonous gas and submarine attacks.

Submarine attacks and poisonous gas was never before used at such a scale before in battles (neither was either available). 

Your answer is 2 because you do keep change flip when you divide fractions

Bis your answer and your welcome