What was the United States’ principal use of Guam in the late 19th century and early 20th century? as a location for U.S. owned tropical fruit farms as a source of rubber and oil for U.S. businesses as a prison camp for soldiers captured in the Spanish-American War as a refueling station for U.S. ships traveling to the Philippines
"As a refueling station for U.S. ships traveling to the Philippines" would be the best option from the list since Guam was only captured in the 20th century, which put the US into two world wars with reach into the Pacific.
