3、用pandas自行构造数据DataFrame，在该数据上分别完成增删改查四个操作，分别对每一个操作加上注释。

好的，以下是对应的代码及注释：

import pandas as pd

# 构造数据
data = {'name': ['Alice', 'Bob', 'Charlie', 'David'], 
        'age': [25, 30, 35, 40], 
        'gender': ['F', 'M', 'M', 'M']}
df = pd.DataFrame(data)

# 输出原始数据
print('Original DataFrame:\n', df)

# 增加数据
new_data = {'name': 'Emma', 'age': 27, 'gender': 'F'}
df = df.append(new_data, ignore_index=True)
print('After adding data:\n', df)

# 删除数据
df = df.drop(index=1)
print('After deleting data:\n', df)

# 修改数据
df.at[2, 'name'] = 'Charlie Brown'
df.loc[df['age'] == 40, 'gender'] = 'F'
print('After modifying data:\n', df)

# 查询数据
result = df.loc[df['age'] > 30]
print('Query results:\n', result)

输出结果如下：

Original DataFrame:
        name  age gender
0     Alice   25      F
1       Bob   30      M
2   Charlie   35      M
3     David   40      M
After adding data:
        name  age gender
0     Alice   25      F
1       Bob   30      M
2   Charlie   35      M
3     David   40      M
4      Emma   27      F
After deleting data:
        name  age gender
0     Alice   25      F
2   Charlie   35      M
3     David   40      M
4      Emma   27      F
After modifying data:
             name  age gender
0          Alice   25      F
2  Charlie Brown   35      M
3           David   40      F
4            Emma   27      F
Query results:
             name  age gender
2  Charlie Brown   35      M
3           David   40      F