A set is defined recursively as follows:

$1.$ Basis step: $(1$ in S$)(3\mathrm{.}5$ in S$)(1$ in S$)(3\mathrm{.}5$ in S$)$

$2.$ Recursive step: if x in Sx in S$,$ then $($x$+1)$ in S$($x$+1)$ in S$.$

Which of the following is the best statement that describes SS$?$

Question $1$Select one:

a$.$

Z$+$SZ$+$S

b$.$

S$$Z$+$S$$Z$+$

c$.$

S$$Z$+$S$$Z$+$

d$.$

S$=$Z$+$S$=$Z$+$

e$.$

Z$+$S