嫁 给 我,好 吗?
你 愿 意 嫁 给 我 吗?
 If your answer is "Yes, I do." 
To reply the first proposal sentence, you need to say: 
好 的。
To answer the second proposal sentence, you can say:  
我 愿 意。
If you want to deny a proposal, you can say:  
对 不 起
And after the apology, you can say whatever you want.
Here is such a romantic and creative proposal, I hope you will enjoy it.
 
