年龄组生育率趋势（组合图）

def solve():
    import pandas as pd
    import matplotlib.pyplot as plt
    import numpy as np
    
    url = 'https://liangdaima.com/static/data/wooldridge/fertil1.csv'
    df = pd.read_csv(url)
    
    age_means = df.groupby('age')['kids'].agg(['mean', 'count']).reset_index()
    fig, ax1 = plt.subplots(figsize=(12,6))
    ax1.bar(age_means['age'], age_means['mean'], color='coral', alpha=0.7)
    ax1.set_xlabel('年龄', fontsize=12)
    ax1.set_ylabel('平均生育数量', fontsize=12, color='coral')
    ax2 = ax1.twinx()
    ax2.plot(age_means['age'], age_means['count'], color='blue', linewidth=2, marker='o')
    ax2.set_ylabel('样本数量', fontsize=12, color='blue')
    plt.title('年龄组生育率趋势', fontsize=14)
    fig.tight_layout()
    plt.show()
    return "可视化代码执行完成"