物质的性质决定它的用途，还决定其保存方法.固体KOH具有以下性质：①白色固体②有腐蚀性 ③易吸收水分 ④能与空气中的二氧化碳反应.实验室中必须将它密封保存的主要原因是           (    )

科学家发现纳米硒（Se）可将汞转化为HgSe，从而消除汞污染。HgSe中汞元素为+2价， 则硒元素的化合价是（　）

⑴Is it hot?____                                                  A. It's on the second floor.

⑵What's the weather like in Beijing?____        B. It's warm and sunny.

⑶Where is the library?____                              C. Yes,we do.

⑷What time is it?____                                      D. No,it isn't.

⑸Do you have a computer room?____            E. It's 6 o'clock.

____?

看图写出相应的韵母和整体认读音节。

  ____ ____         ____ ____         ____ ____