The correct option is C Some of the most important long term or structural causes of the First World War were the growth of nationalism across Europe, escalation in territorial disputes, intensified and intricate system of alliances, and a heightened race for arms and the decline in mutual trust between nations especially neighbours and a drop in mutual regard
A. no need for and after Europe, disputes, while and is required after alliances
B: ‘and’ is required after race for arms
C: correct choice
D: ‘and’ is required after race for arms
E: The choice wants to say that there is only one primary reason for the war and all others are secondary factors; So a plural verb ‘were’ is inappropriate.