Speaker A. Did you hear about those people who got hurt when going mountain climbing I think they shouldn't allow people to go mountain climbing. It's too dangerous.Speaker B: ______

A．I couldn't agree more. I can't understand why anyone wants to get to the top of a mountain.

B．I couldn't agree less. Mountain climbing is actually more dangerous than surfing.

C．I'm sorry to hear that. Where did you get the news

D．No, I have decided not to go mountain climbing with my friends next month.

有关物质的转化关系如图所示：其中X、Y为两种气态单质，Z为常见金属单质；A为最简单的有机化合物，B、C、D为氧化物、M是一种有毒的气体。

回答下列问题：

（1）写出下列物质化学式

C：      D：      Y：     

（2）反应①、② 、③、④中属于化合反应的为        （填序号，下同），属于置换反应的为          ；

（3）写出反应①的化学方程式                                         ；

（4）若图中的浅绿色溶液能与硝酸银生成不溶于稀硝酸的白色沉淀，则反应④的化学方程式                    。