The correct answer to this open question is the following.
Although you forgot to attach the options for this question we can say the following.
The cause of the Spanish-American War that best explains why the sinking of the USS Maine led America to declare war on Spain was Manifest Destiny.
President McKinley could justify entering the war with the sinking of the USS Maine that was anchored in the harbor of Havana, the capital city of the Island of Cuba, This was part of the imperialistic desire of the United States government supported by Manifest Destiny, the idea that the United States had the divine right to expand its territory.
President McKinley tried to stay away from the conflict between Cubans and Spaniards, but there was so much pressure from the American people and the US newspapers that published reports about Mckinley as a weak leader. That is why after that above-mentioned incident, the US President asked the US Congress for a declaration of war, and the Spanish American War started.