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D.Members of an alliance had to defend each other if one went to war.

D.

Explanation:

How did Alliance Systems cause WWI? Secret alliances were formed prior to the outbreak of the war. After the Assassination of Franz Ferdinand the Archduke of Austria-Hungary the alliance systems went into effect leading to many nations protecting one another (i.e. Russia protecting Serbia from Austria-Hungary). Alliances prevented larger, stronger states from waging war on the smaller, weaker states.

donald carl johanson (born june 28, 1943) is an american paleoanthropologist. he is known for discovering – with yves coppens and maurice taieb – the fossil of a female hominin australopithecine known as "lucy" in the afar triangle region of hadar, ethiopia.

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