${?}^7$ point

$8.$ The largest ungrounded secondary conductor supplied by a separately derived system is $2,500$kcmil XHHW copper total $($five $500$kcmil XHHW copper conductors in parallel per phase$).$ If the system is grounded by use of a ground rod type electrode, what size copper grounding electrode conductor is required?

a$.8$ AWG

b$.6$ AWG

c$.\frac{1}{0}$ AWG

$q,$ d$.3/0$ AWG