The correct option that explains why President Abraham Lincoln is an important symbol in World War I is:
C stood up for equality for different races.
Lincoln is best known for his Emancipation Proclamation and efforts to abolish slavery, which laid the groundwork for civil rights and equality. His legacy would have influenced thoughts on equality during World War I, where issues of race and equality were prominent in both the military and society at large. The war also saw significant contributions from African American soldiers, reflecting the ongoing struggle for equality that Lincoln championed.