他们对此现象进行了讨论，认为这是由于冰的熔化和凝固引起的．关于冰熔化的原因．他们提出了以下三种猜想：

猜想l：冰块的厚度小．

猜想2：金属丝的温度低．

猜想3：金属丝对冰块的压强大．

某电脑公司有A型、B型、C型三种型号的电脑，其中A型每台5000元、B型每台4000元、C型每台3000元，某中学现有资金100000元，计划全部用从这家电脑公司购进30台两种型号的电脑，请你设计几种不同的购买方案供这个学校选择，并说明理由．

已知：“碱浸”时，NaOH溶液浓度越大越粘稠，越容易生成铝硅酸钠沉淀。

阅读下面材料，在空白处填入适当的内容（1个单词）或括号内单词的正确形式。

    In order to know a foreign language thoroughly （完全地） , four things are necessary. Firstly, we must understand the language when we hear ____ spoken. Secondly, we must be able to speak it ____ (correct) with confidence and without hesitation（犹豫）. ____ we must be able to read the language, and fourthly, we must be able to write it. We must be able to make sentences that are grammatically correct.

    There is no easy way to success in language learning. ____  good memory is of great help, but it is not enough only ____ ( memorize) rules from a grammar book. It is not much use learning by heart long list of words and ____ meaning, studying the dictionary and so on. We must learn by using the language. ____ we are satisfied with only a few rules we have memorized, we are not really learning the language. “Learn through use” is a good piece of ____ (advise) for those ____ are studying a new language. Practice is important. We must practise speaking and ____ (write) the language whenever we can.