For the data given below, if the time series was assumed to be stable, what would the naive forecast be for the next period?

Period

Demand

$1$

$58$

$2$

$61$

$3$

$60$

$4$

$61$

a$.$

$61$

b$.$

$60\mathrm{.}5$

c$.$

$58$

d$.$

$62$

e$.$

$59\mathrm{.}5$