The slope between points A and C is $\_\_\_\_\_\_\_\_\_\_,$ and this slope is called the $\_\_\_\_\_\_\_\_\_\_.$

A$.)$

$1\mathrm{.}8$; marginal rate of transformation $($MRT$)$

B$.)$

$1\mathrm{.}2$; marginal rate of transformation $($MRT$)$

C$.)$

$1\mathrm{.}8$; marginal rate of substitution $($MRS$)$

D$.)$

$1\mathrm{.}2$; marginal rate of substitution $($MRS$)$