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