The correct answer is B. cov().
The covariance between two variables is a measure of how much they vary together. It is calculated by taking the average of the product of the deviations from the mean for each variable.
In Pandas, the cov() method can be used to calculate the covariance between two numerical columns in a DataFrame. The syntax is as follows:
df.cov(column1, column2)
For example, if we have a DataFrame with two columns, x and y, we can calculate the covariance between them as follows:
df.cov(x, y)
This will return a number that represents the covariance between the two columns.
The other options are incorrect. The sum() method is used to calculate the sum of the values in a column. The median() method is used to calculate the median of the values in a column.