Choose the statement that best expresses the central idea of this selection.
A. Some military schools continued to exclude women long after others graduated their first female classes.
B. Since World War II, gender discrimination in the U.S. military has declined to almost imperceptible levels.
C. Women have long-served the U.S. military in crucial roles, but obstacles to equal opportunity remain.
D. More than 10,000 women served in the Vietnam War, but little is known about their service in this conflict.