Let $f(n)$ and $g(n)$ be functions mapping positive integers to positive real numbers. Which of the following is a definition of the big$-$Oh notation.

$f(n)$ is $O(g(n))$ if there is a real constant $c>0$ and an integer constant $n_{0}1$ such that $f(n)=c*g(n),$ for $n{n}_0.$

$f(n)$ is $O(g(n))$ if there is a real constant $c>0$ and an integer constant $n_{0}1$ such that $f(n)=c*g(n),$ for $n{n}_0.$

$f(n)$ is $O(g(n))$ if there is a real constant $c>0$ and an integer constant $n_{0}1$ such that $f(n)c*g(n),$ for $n{n}_0.$

$f(n)$ is $O(g(n))$ if there is a real constant $c>0$ and an integer constant $n_{0}1$ such that $f(n)c*g(n),$ for $n{n}_0.$