Peter has $$20$$ ounces of a $$20\textbackslash\%$$ salt solution. How many ounces of salt should he add to make it a $$25\textbackslash\%$$ solution? 
选项为:A:$1$ ounces  B:$$\dfrac{4}{3}$$ ounces  C:$4$ ounces  D:$5$ ounces  请回答其中一个选项.