The correct answer is D) "the debate over the spread of slavery grew more bitter."
An outcome of California's application for statehood was "the debate over the spread of slavery grew more bitter."
California became part of the United States territory after the Mexican-American War Both countries signed the treaty of Guadalupe-Hidalgo in February 1848, in which Mexico also lost the territories of Utah, Colorado, Arizona, Nevada, and New Mexico.
The next year, California wanted to be a state of the Union, and the issue of slavery increased. After much debate on Congress, California became the 31st state of the Union on September 8, 1850. It entered as a free non-slavery state.