Enough sleep is important to health. The amount of sleep（21）depends on the age of the per-son and the conditions in which sleep（22）. The young may need more sleep than the old, but generally eight hours are enough for the health of grown-ups. Some can（23）with less than this amount but（24）may need more. Every person knows his own need. It is then a matter of how to（25）it. Sleep should always be enough to make one relaxed(松弛)and ready for（26）work.
Fresh air is（ 27）to sound sleep(酣睡). It is not without reason for some people to（28）that it is practical to sleep in the open air.（29）a person can keep himself warm, out-of-door sleeping probably gives the body（30）complete relaxation.
Ability to sleep is largely a habit. The conditions referred to only lead to sleep. Out-of-door（ 31）,a good habit of regular drinking and the avoidance of late eating and（32）are all helpful to sound sleep. Such factors are largely within the control of any person. A bath at（33）, neither hot nor cold but of（34）temperature, may be helpful to sleep. Sleeping pills should never be taken except when suggested by（35）.
第（31）题选
此处意思是“户外的锻炼”，用exercises。trip旅行；housework家务，均与句意无关。walk“散步”，仅是一种锻炼的方式。
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_______。
