"The plane _______ in a minute. Please fasten your safety belts and remain on your seats until it has

landed," the stewardess announced in a sweet voice.     [ ]

A. is going to land    

B. will land  

C. is about to land  

D. will be landing

实验桌上放置一瓶无色无味的气体（如图所示），请你猜想一下是什么气体？

（1）写出两种可能性。

（2）并对其中一种猜想用实验的方法验证，写出实验的操作步骤、现象和结论。