The correct options are
C Entry of the USA changed the course of the war.
D Germany occupied France and Belgium during the war.
The First World War was fought from 1914 to 1918, draining Europe of its resources. Germany fought on the side of Central Powers, not the Allies. In the initial years of the war, Germany had the upper hand over the Allies as it occupied France and Belgium. With the entry of the USA in 1917, the tables turned. Germany, along with the Central Powers, lost the war in November 1918.