(IM POSTING THIS TO GIVE FUTURE PEOPLE THE RIGHT ANSWER AS IT HASNT BEEN ASKED BEFORE) Countries encouraged nationalism leading up to World War I by asking citizens to

A. burn crops in their own country to keep food from the enemy.
B. cooperate with other countries to prevent conflict.
C. buy products from other countries to boost the economy.
D. support their own country in times of need or conflict.

For anyone who needs this answer or for future math students... The answer is D: support their own country in times of need or conflict.