"It' s no use, Mum, "said Johnny．"I' m just no good at dancing．"
"You' ve got to keep trying．Tonight will be 21 ,dear．Try a turn with that pretty Lisette．"
Johnny 22 ．Every Saturday night used to be the best of the week．He and his parents went to the 23 at the Club, where his hero, Alcide, played the accordion(手风琴) with the band．But lately everything had changed．Now that Johnny was older, he was 24 to dance with a girl!
25 Johnny and his parents arrived at the Club, music had already started．Johnny got up his 26 to approach Lisette．"May I have this dance?" Johnny asked．"That's all right," said Lisette．
Johnny struggled to keep up with Lisette' s 27 steps, but he was always one beat behind her．Then Johnny heard his friend Pierre say," Look! Johnny has two left feet!" Laughter burst from the crowd．
Johnny 28 and ran outside, determined never to go to another dance．
The next Saturday, Alcide drove to Johnny' s house for some potatoes．He happened to hear Johnny playing the accordion．Alcide' s eyes 29 "Bring that accordion and play some songs tonight,"Alcide said．Then he drove off, leaving Johnny staring open-mouthed 30 him．
At the Club,Johnny scanned the crowd for Lisette and 31 her．The band played for a long time before Alcide said," Dear friends, I got a 32 for you tonight．Young Johnny is going to join us!"
Trembling ,Johnny stepped up on the platform, his eyes on the floor．He began to play, and the band joined in behind him．When the song ended, he heard cheers．Johnny kept playing until the dance was 33 ．" You did a fine job tonight．Play with us again next Saturday night," Alcide said．"Yes, sir!"
said Johnny． 34 he went outside, Johnny saw Lisette and her friends near the door．Lisette stepped forward, smiling," You played really good tonight!" she said．
"Thank you," Johnny blushed (脸红)．As he walked on, Pierre 35 moved out of the way for him to pass．
Johnny patted his accordion．Come to think of it, in his whole life, he had never once seen Alcide out on the dance floor．
第（21）题答案
推理判断题。从第一段Johnny不擅长舞蹈和下一句可推断出今晚与往常不同。
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_______。
