如图是硝酸钾和氯化钠的溶解度曲线．

（1）两种物质中．溶解度受温度影响较小的是____ ．

（2）使接近饱和的氯化钠溶液变为饱和溶液的一种方法是____ ．

（3）60℃时，硝酸钾饱和溶液中溶质、溶剂的质量比是____ ．

（4）60℃时，硝酸钾饱和溶液中溶有少量的氯化钠．提纯硝酸钾应采用的方法是____ ．

   Who are the top students in the world, do you know? Last week the Organization for Economic Co-operation Development (经济合作与发展组织) picked the best students in the world. They are Finnish (芬兰的). The OECD gave a test to 280 000 15-year-old students from more than 40 coun­tries and regions (地区) last year. The OECD wan­ted to know how well students were doing at school.
   Finnish students were No. 1 in the reading test and second in maths after Hong Kong students. Those from Japan and Finland were top in science. In the problem solving, Finnish students came sec­ond to those from South Korea. The test also showed Finland had more top students than the other countries.
   Finns (芬兰人) of your age have done a really good job but don't have a sense of envy. You can learn from them. Most Finnish students make good use of the Internet. Of course not for computer games, but for doing more exercises and finding out more information.
Libraries are also important. Finland spends a lot of money on them. Many students have a free card. They read for at least one or two hours a day.
   What do you usually do on the Internet? How often do you go to libraries?

世界上水量最大、流域面积最广的河流是(    )

— Only ____ (三)stops away.