根据下面资料，回答40-42题
Scientists have long tried to be able to know more about floods．So far, the best that scientists can do is to recognize the conditions for flooding．
Although deep snow alone seldom causes floods, when it occurs together with heavy rain and sudden warmer weather, it can lead to serious flooding．If there is a fast snow melt (融化) on top of frozen or very wet ground, flooding is likely to occur．Melting snow also causes high water levels in rivers．
Whenever rivers are already at their highest possible levels, heavy rains will result in the rivers' flooding the nearby land．
Rivers covered in ice can also lead to flooding．When ice begins to melt, it breaks into large pieces．
These pieces of ice move and float down the river．They can block the river, causing the water to rise and flood the land up the river．If the ice dam (坝) breaks suddenly, the large quantity of water held behind it can flood the areas down the river too．
Broken ice dams are not the only problem that can cause flooding．When a large human-made dam breaks or fails to hold the water collected behind it, it will also cause serious damage．
Although scientists cannot always know when floods will occur, they do know a great deal about when floods are likely, or probably, going to occur．
When will deep snow lead to floods
事实细节题。根据第二段g一句可知，虽然厚厚的积雪很少引发洪水，但当遇到大雨，再加上天气突然转暖，就会引发严重的洪水。故本题选C。
把10gMgCl2和MgSO4的混合物溶于适量水中，滴加2mol／L的BaCl2溶液至沉淀完全，共消耗BaCl2溶液25mL。求混合物中MgCl2和MgSO4的质量各是多少克
固定在匀强磁场中的正方形导线框abcd，各边长为1．其中ab是一段电阻为R的均匀电阻丝，其余3边均为电阻可忽略的铜线。磁场的磁感应强度为B，方向垂直纸面向里。现有一与ab段的材料、粗细、长度都相同的电阻丝PQ架在导体框上，如图所示。PQ以恒定速度方向如何
一小物块以速度v0=10m／s沿光滑地面滑行，然后沿光滑曲面上升到顶部水平的高台上，并由高台上飞出，如图所示。问当高台的高度h多大时，小物块飞行的水平距离最大这个距离是多少(g=10m／s2)
某晶体盐的水溶液呈浅绿色，在此溶液中通入氯气，溶液变为棕黄色，把所得棕黄色溶液分成两份：一份加入KSCN溶液，溶液变深红色；另一份加入BaCl2溶液，产生不溶于稀HNO3的白色沉淀，则该晶体盐的化学式是_______。
欲除去乙烷中的乙烯，可将混合气体通过盛有_______的洗气瓶；欲除去乙炔中的硫化氢，可将混合气体通过盛有_______的洗气瓶。
浓硝酸常盛装在棕色瓶中，且贮放在冷暗处，原因是_______，
碳酸氢钠溶液和烧碱溶液反应的离子方程式为_______。
常温下，氨水中存在的离子有_______。
在酸或碱存在的条件下，甲酸甲酯跟水发生水解反应的化学方程式为_______。
有下列几种气体：H2、O2、HCl、NO、NH3、CH4，其中通常情况下能用来和水做“喷泉”实验的是_______。
