A project leader has realized that two activities in the project cannot be done at the same time because not enough resources are available. Activity $3$ is critical and has a duration of $5$ days. Activity $4$ has $2$ days of slack and a duration of $2$ days. How will the project leader decide which activity should be scheduled first?

The activity with the most slack

The activity with the least slack

The activity with the smallest duration

The activity with the lowest identification number

The activity with the highest cost