Question $5$

What is the default behavior of the 'mean$()\text{'}$ function in R when calculating the mean of a numeric vector with missing values $($NA$)?$

It replaces missing values with the mean of the non$-$missing values.

It ignores missing values and calculates the mean of the remaining values.

It returns an error.

It replaces missing values with $0$ and calculates the mean.

None of the above.