1 . Consider strings of length $61$, in which each character is one of the characters $a,b,c,d,e$. How many such strings have exactly $15$ letters $e$?
(a)
$\binom{61}{15}\cdot 4^{46}$
(b)
$\binom{61}{15}\cdot 5^{46}$
(c)
$5^{15}\cdot 4^{46}$
(d)
$\binom{61}{5}\cdot 4^{46}$
(e)
$\binom{61}{5}\cdot 5^{46}$