1 . Consider strings of length $86$, in which each character is one of the characters $a,b,c,d,e$. How many such strings have exactly $18$ letters $e$?
(a)
$5^{18}\cdot 4^{68}$
(b)
$\binom{86}{5}\cdot 4^{68}$
(c)
$\binom{86}{18}\cdot 4^{68}$
(d)
$\binom{86}{18}\cdot 5^{68}$
(e)
$\binom{86}{5}\cdot 5^{68}$