Which statement best summarizes the effect diseases had on the spanish-american war?
when american troops returned home, diseases caused epidemics throughout the united states.
the spanish-american war marked the first time biological weapons were used in warfare.
diseases shortened the war by forcing the united states to retreat after epidemics spread throughout the army.
more american soldiers were killed by diseases such as yellow fever and malaria than were killed in battle.
i think this is d

The correct answer is D. More American soldiers were killed by diseases such  as yellow fever and malaria than were killed in battles

Explanation:

The Spanish-American war was a conflict between the U.S. and Spain in 1898  as the U.S. intervened in the Cuban War of Independence as Cuba was still under the rule of Spain. During this war, around 2061 American soldiers died as a result of diseases, mainly due to yellow fever and Malaria which was transmited by Mosquitos when the American troops invaded Cuba, additionally around 300 soldiers died during Battles. This implied more soldiers (around 2061) died as a result of diseases (mainly malaria and yellow fever) than those that were killed in battle (around 300), this was also the main reason American troops decided to leave Cuba on August 4th of 1898.

c it says nothing about connecting those 2 seas.