the corresponding fault tree is shown in Fig. $2.$

$1.$ If all of the units have the same failure rate and if you have only limited resources to provide redundancy of only one unit, for which unit will you provide redundancy?

Provide your intuitive argument to justify your answer; you do not need to perform calculations.

$2.$ Consider that units $1$ and $2$ have a failure rate of $10-*$hr$-1,$ units $3,4,5$ and $6$ have a failure rate of $10-3$hr$-1$ and unit $7$ has a failure rate of $10-5$hr$-1.$ If you have an option to provide redundancy for only one unit, which unit will you provide the redundancy for? Justify your answer with proper calculations. $($Hints: You can perform calculations for a certain operational time, e$.$g$.1000$