People were not allowed to enter the reading room because it _______. A. had been painted B. was being painted C. was painting D. painted 答案:B 解析: 略小明在厨房中发现: (1)壶里的水烧开以后,壶嘴上方冒出一团团“白气”。这“白气”实质上是一些 。小明仔细观察又发现:“白气”从喷出到消逝要经历三个物理过程。①靠近壶嘴的地方,我们什么也看不见。这是因为 ,仍然保持气体状态。②水蒸气离开壶嘴一段距离以后, ,形成“白气”。③“白气”进一步上升,分散到干燥的空气中,发生 现象,我们又什么也看不见了。(2)冬天,在炉子上烧菜的时候,火焰熄灭前、后一瞬间会出现如图所示的两种情景,你可以确定 是火焰熄灭后的图片。