$9.$ In a packed column, if the gas flow rate is $0\mathrm{.}8$ m$\backslash (^3\backslash )/$s and the liquid flow rate is $0\mathrm{.}4$ m$\backslash (^3\backslash )/$s$,$ the gas$-$to$-$liquid ratio is $\_\_\_\_\_.$

$-$ a$)0\mathrm{.}5$

$-$ b$)1$

$-$ c$)2$

$-$ d$)0\mathrm{.}8$