清洁显微镜镜头时，除去污物的正确方法是（　　）

中国近代思想主要经历了“师夷长技以制夷”、“中体西用”、“维新变法”、“民主共和”、“民主与科学”及“马克思主义”的演进过程。这些思想反映的共同主题是（  ）  

某化学课外活动小组研究乙醇氧化的实验并验证其产物，设计了甲、乙两套装置（图中的夹持仪器均未画出，“△”表示酒精灯热源），每套装置又可划分为①、②、③三部分．仪器中盛放的试剂为：a﹣无水乙醇（沸点：78℃）；b﹣铜丝；c﹣无水硫酸铜；d﹣﹣新制氢氧化铜悬浊液．

用括号内所给动词的适当形式填空。
(1)In the past three years, my home town ____ (change) a lot. already.
(2)It's hard to say what____  (happen) in 100 years in our country.
(3)They____ (not travel)to Shanghai next week, are they?
(4)The students____ (chat) from 6 to7 yesterday evening.
(5)When I got to the station yesterday morning, my friends____ (wait ) for me at the entrance.
(6)If it____  (not rain) tomorrow, we’ll go hiking.
(7)He____  (not write) a letter to his mother yet. He has to do that soon. His mother misses him very much.
(8)Would you please____ (not make) such a big noise. The baby is sleeping.
(9)It's a long time since we ____ (meet) last time, isn't it?
(10)How many times____ the girl____ (forget) to take the keys to her home?
    At least three times.
(11)You must spend as much time as you can ____ (practise) playing the piano.
(12)They____ (live) in Wuxi since they were born.