Imagine we have a pandas dataframe we have named $\text{'}$df$\text{'}.$

The dataframe consists of $2$ columns.

"col$1"$ is $30$ values long, and is a random mix of the letters $\text{'}$a$\text{'},\text{'}$b$\text{'},$ and $\text{'}$c$\text{'}.$

"num$1"$ is also $30$ values long, and is a random set of numerical data $($all integers$).$

Which of the following would give you the mean of the numerical $($num$1)$ column, grouped by the values from column "col$1"?$

groupby num $1$