The Allied Powers included

A. Germany, Austria-Hungary, the Ottoman Empire, and eventually Bulgaria

B. Germany, Austria-Hungary, and eventually Italy

C. France, Great Britain, Germany, and eventually the Ottoman Empire

D. France, Great Britain, Russia, Italy, and eventually the United States

Reasons for joining WWI:Serbia (Dispute over Balkans)

Russia (Allied with Serbia)

Great Britain (Allied with Belgium)

France (Allied with Russia)

Belgium (Germany invaded to get to France) so the best answer is D

if you wanna know the Axis, and centeral here ya go

Reasons for joining WWI:Austria-Hungary (Dispute over Balkans)

Germany (Allied with Austria-Hungary)

Bulgaria (Allied with Germany)

Ottoman Empire (Allied with Austria-Hungary)

Neutral:Italy (Entered war in 1915 as an Allied Power)

United States (Entered war in 1917 as an Allied Power)

Spain

Netherlands

Norway

Sweden

Switzerland