Luna asks her grandmother how old she is, and her grandmother replies: "if you multiply your age by $5$ and then add by $7$, then you would be my age." Luna is $12$ years old. Which of the following is an equation that correctly represents Luna\textquotesingle s grandmother\textquotesingle s age? Let $x$ represent grandmother\textquotesingle s age. 
选项为:A:$x = 12 \times 5 - 7$  B:$x ~= 12 \times 5 + 7$  C:$x + 1= 12 \times 5 + 7$  D:$ 12 \times 5 + 7 - 1$  请回答其中一个选项.