While reading from a CSV file, to use a column's values as index labels, argument given in read_CSV() is :

1. index
2. index_col
3. index_values
4. index_label

While writing a DataFrame onto a CSV file, which argument would you use in to_csv() for NaN values' representation as NULL ?

1. NaN = NULL
2. na_rep = NULL
3. na_value = NULL
4. na = NULL

In pandas.read_sql(<A>, <B>), <A> is

1. connection name
2. table name
3. SQL query string
4. database name

In pandas.read_sql(<A>, <B>), <B> is

1. connection name
2. table name
3. SQL query string
4. database name