1 .
Consider strings of length 70, in which each character is one of the letters $a,b,c$. How many
such strings have exactly 1 letter $c$?
(a)
$70 \cdot 2^{70}$
(b)
$70 \cdot 2^{69}$
(c)
$70 \cdot 3^{69}$
(d)
$70 \cdot 3^{70}$