1 . Consider strings of length $78$, in which each character is one of the characters $a,b,c,d,e$. How many such strings have exactly $20$ letters $e$?
(a)
$5^{20}\cdot 4^{58}$
(b)
$\binom{78}{5}\cdot 4^{58}$
(c)
$\binom{78}{5}\cdot 5^{58}$
(d)
$\binom{78}{20}\cdot 5^{58}$
(e)
$\binom{78}{20}\cdot 4^{58}$