$3\mathrm{.}1$ The work breakdown structure $($WBS$)$ for building a house $($levels $1$ and $2)$ is shown below:

a$)$ Add two level$-3$ activities to each of the level$-2$ activities to provide more detail to the WBS$.$

b$)$ Select one of your level$-3$ activities and add two level$-4$ activities below it$.$