$1\mathrm{.}1.$ If the concrete characteristic compressive strength $f_c$ is $65$ MPa $,$ according to AS $3600-$

$2018,$ how much is the ${}_2$ value?

A$.0\mathrm{.}805$

B$.0\mathrm{.}7525$

C$.0\mathrm{.}67$

D$.0\mathrm{.}85$