Average daily demand for a product is normally distributed with a mean of $5$ units and a standard deviation of $1$ unit. Lead time is fixed at four days. How much safety stock changes if the service level is raised from $80\%$ to $90\%?$ Decreases by almost $2$ units.

Decreases by almost $1$ unit.

Increases by almost $1$ unit.

Increases by more than $3$ units.

Increases by almost $2$ units.