南方地区农作物一年两熟至三熟的主要原因是（    ）

活动与分析 甲组同学没有观察到明显现象，认为稀盐酸和氢氧化钠溶液没有发生化学反应: 乙组同学观察到溶液中产生白色沉淀，得出了二者能够发生反应的结论。该反应的化学方程式

为(1)____请你对甲组同学的结论作出评价并说明(2)____理由;有同学提出甲组同学只需向氢氧化钠溶液中先加入(3)____就可通过颜色的变化证明二者是否发生反应。总结与交流：通过上述探究，同学们总结出: 在确定物质间是否发生反应时不能只根据象来判断，往往还要通过验证(4)____来得出正确结论。

深入探究：乙组同学把废液过滤后，将滤液倒入盛有甲组废液的废液缸中，一段时间后观察到溶液中有气泡冒出。同学们好奇，最终废液中含有哪些溶质?

猜想与假设：甲组同学认为废液中溶质为: NaCl、Ba(OH)₂、BaCl₂ ;

乙组同学认为废液中溶质为: NaCl;

你认为还可能有哪几种情况，分别为(5)____

反思与评价：请评价甲组同学的猜想并说明理由(6)____

实验与探究：同学们最后只用一种试剂就得出了正确结论，你认为该试剂是(7)____

如图所示为汽车比赛的水平环形赛道，圆心为O，内外环赛道半径分别为r₁和r₂，某汽车沿两环形赛道行驶时，路面对汽车轮胎的最大静摩擦力相同，当汽车分别沿内环和外环赛道以不打滑的最大速率绕赛道一圈，所需要时间分别为t₁和t₂，则（   ）

    The Descendants of the Sun(太阳的后裔) that really ____ (earn) the praise(reputation)of K－drama fans. It made its debut(首映) on February 24, 2016 with an average of 13 percent in the Seoul National Capital Area. The next night, ratings ____ (go) up an average of two percent. ____ (apparent), those two episodes set up Descendants of the Sun as it dominated the competition with its third episode. ____ nationwide and Seoul National Capital Area for both TNmS Ratings and AGB Nielson, the K－drama earned over 20 percent viewership ratings(收视率).

    For those ____ do not know what Descendants of the Sun is about, it is a drama about the love of people who get ____ (close) as they learn to be considerate of each other in desperate times. It is also about the sacrifices made by people who throw themselves ____ natural disasters. Captain Yoo Shi Jin(柳大尉) (Song Joong Ki宋仲基) is the team leader of the Special Warfare Command of the United Nations Peacekeeping Troops. By request of the UN, he is ____ (station) in the war-torn country of Uruk(乌鲁克). ____he meets Kang Mo Yeon(姜暮烟) (Song Hye Kyo宋慧乔), a volunteer doctor with Doctors Without Borders.____they work alongside each other, they clash and fall in love.

小明用焦距为10cm的凸透镜探究凸透镜成像的规律，他将烛焰放在距凸透镜15cm的位置，调节光屏位置，可以得到一个清晰的倒立、____（选填“等大”、“放大”或“缩小”）的实像，利用这个原理可以制成 ____．实验中他不慎用手指尖触摸到了凸透镜，此时光屏上 ____（选填“会”或“不会”）出现手指尖的像