Amy mixes $$10$$ grams of a $$20\textbackslash\%$$ sugar solution and $$40$$ grams of a $$25\textbackslash\%$$ sugar solution together. After~\uline{~~~~~~~~~~}~of water evaporates, the percent concentration of solution is $40\textbackslash\%$. 
选项为:A:$$15$$ grams  B:$$18$$ grams  C:$$20$$ grams  D:$$25$$ grams  请回答其中一个选项.