1 . How many strings can be obtained by rearranging the letters of the word POOPERSCOOPER
(a)
${{13}\choose{4}}{{9}\choose{3}}{{6}\choose{2}}{{4}\choose{2}}{{2}\choose{1}}$
(b)
$4!3!2!2!1!1!$
(c)
${{13}\choose{4}}{{9}\choose{3}}{{6}\choose{2}}{{4}\choose{2}}$
(d)
$13!$