Each A $($finished good$)$ requires $1$ of component B and $2$ of component C$.$ Each B requires $2$ of part D and $1$ of part E; and each C requires $1$ of part D and $1$ of part F$.$ If the demand for product A is $30$ units, and there are $10$ units of B on hand and none of C$,$ how many units of part D will be needed?

A$.80$

B$.60$

C$.100$

D$.120$

Answer Key:C