$1)$ When the conventional retail inventory method is used, markdowns are commonly ignored in the computation of the cost$-$to$-$retail ratio because

a$)$ This tends to give a better approximation of the lower$-$of$-$cost$-$or$-$market

b$)$ This tends to result in the showing of a normal profit margin in a period when no markdown goods have been sold

c$)$ There may be no markdowns in a given year

d$)$ Markups are also ignored