ফাংশনের ডোমেন ও রেঞ্জ {$a, b, c, d$} হলে কোনটি এক-এক ফাংশন?

$f(a) = b, f(b) = c, f (c) = d, f(d) = a$

$f(a) = b, f(b) = c, f (c) = b, f(d) = a$

$f(a) = b, f(b) = c, f (c) = d$

$f(a) = b, f(b) = c, f (c) = d, f (c) = a$