北路园小区有两居室320套，三居室的套数是两居室的 $\frac{3}{4}$ ，一居室的套数是三居室的 $\frac{2}{3}$ ，这个小区有一居室____套？

体液中Ca²⁺含量太低时，神经、肌肉的兴奋性升高而出现抽搐。这一事实说明Ca²⁺的作用之一是

    In order to know a foreign language thoroughly, four things are necessary. Firstly, we must understand the language when we hear ____ spoken. Secondly, we must be able to speak it ourselves correctly with ____ (confident) and without hesitation. Thirdly, 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 ____ (grammatical) correct.

    There is no easy way to success ____ language learning. ____ good memory is a great help, but it is not enough only ____(memorize) rules from a grammar book. It is not much use learning by heart long lists of words and ____ meanings, 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 advice for those ____ are studying a new language. Practice is important. We must practise speaking and ____(write) the language whenever we can.