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Empress Wu was the first female ruler of China. Why was she so ruthless in her personal relationships?

1.Empress Wu never learned how to have closes personal friends, so she treated everyone with cruelty.
2.Empress Wu did not have the time or energy to get close to anyone emotionally--she had a county to rule.
3.Empress Wu was more ruthless because she was a woman who had a great deal of power.
4.Like any dynasty ruler, Empress Wu was always worried about being overthrown by someone close to her.