He was a professor. At the age of 90, he still worked eight hours every day regardless 61 the weather. His secretary said: “He was extremely old, but he forced himself to walk from his livi
---It is required that you____ change the plan. ---Oh, no! Why____ I follow you again? A. must, must B. can, need C. need, should D. should, must
在室温下，下列五种溶液: ①0.1mol/L CH3COONa ②0.1mol/L CH3COONH4 ③0.1mol/L NH4HSO4 ④0.1mol/L NH3·H2O和0.1mol/L NH4Cl混合液 ⑤0.1mol/L NH
工业上冶炼金属一般用热分解法、热还原法和电解法，由于金属的化学活动性不同因此采用不同的冶炼方法。你认为选择的原则主要是依据A.金属阳离子
（08年长郡中学一模理）（12分）已知在多面体ABCDE中，AB⊥平面ACD，DE∥AB，AC = AD = CD = DE = 2，F为CD的中点．（Ⅰ）求证：AF⊥平面CDE；（Ⅱ）求平面ABC和
下列对无线电广播要对电磁波进行调制的原因的说法正确的是( ) A.经过调制后的高频电磁波向外辐射能量的本领更强 B.经过调制后的电磁波在空间
下列有关溶液性质的叙述，正确的是（ ）A.室温时饱和的二氧化碳水溶液，冷却到0 ℃时会放出一些二氧化碳气体B.20 ℃，100 g水中可溶解34.2 g KCl，
下列命题正确的个数是（ ）①“在三角形ABC中，若,则”的逆命题是真命题；②命题或，命题则是的必要不充分条件；③“”的否定是“”；④
