如何在Matplotlib图中单独标记条形图？

import matplotlib.pyplot as plt
import numpy as np

categories = ['A', 'B', 'C', 'D', 'E']
values = [10, 15, 7, 12, 9]

plt.bar(categories, values)

index = 2  # 要标记的条形图的索引
label = 'Max'  # 标记的文本
value = values[index]  # 标记的值

plt.annotate(label, (index, value), xytext=(index, value + 1), ha='center', color='red', weight='bold')

plt.show()