Given the task definition and input, reply with output. In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].

(CNN) That women have long been paid less than men for the same job is not news. Susan B. Anthony advocated equal pay for equal work back in 1868. It's been nearly 150 years since then; we've come very far, haven't we? If only. In fact, as we observe National Equal Pay Day on Tuesday, the news remains discouraging. I study executive compensation, and I can confirm that even the most powerful women in America are still paid less than their male counterparts. But there is some good news. Some U.S. companies have discovered a way to close the gap: putting more women on their boards of directors.Mary Ellen Carter: On National Equal Pay Day, grim truth is women still make less than men. But there's good news for corporate womenShe says research shows pay gap lower when women serve on corporate boards; effect spreads to company's other executive level women 
 Question:Three women now hold four stars in the _ military.

U.S.