题目

What makes a gift special? Is it the price you see on the gift receipt? Or is it the look on the recipient's face when they receive it that determines the true value? What gift is worth the most? This Christmas was debating what to give my father. My dad is a hard person to buy for because he never wants anything. I pulled out my phone to read a text message from my mom saying that we were leaving for Christmas shopping for him when I came across a message on my phone that I had locked. The message was from my father. My eyes fell on a photo of a flower taken in Wyoming, and underneath 关于化学反应xA+yB═mC+nD，有下列说法：①化学计量数x与y的和一定等于m与n的和；②若A、C为单质，B、D为化合物，则该反应一定是置换反应；③若B是碱，则C和D中一定有一种是盐；④若A和B各取10g混合，使其充分反应后，则C和D的质量总和一定为20g；⑤若B和D都是盐，则该反应一定是复分解反应；⑥若C和D分别为盐和水，则该反应一定是中和反应，其中正确的是（ ）A．①②④⑤B．②③⑤⑥C．只有②③D．只有②