Grammar
Builiding word with 化
In level 3 lesson 4, we saw character 化 huà in the word 文化 wénhuà "culture", literally "transformation through writing". 化 huà means "transform / transformation". We can easily guess the words ending with 化:
国际化 international + transformation = internationalization
现代化 modern + transformation = modernization
Classifier 所
In level 2 lesson 6, we saw character 所 suǒ in the word 所以 suǒyǐ "that's why". Alon, character 所 means "place", but it is no longer used with this meaning in modern Chinese. However it is used as a classifier for buildings, mainly for schools:
一所高中 a high school
这所大学 this university
Differences between 周 and 星期
In level 3 lesson 8, we saw the character 周 zhōu in the word 周末 zhōumò "weekend". We then saw that it could be used to form words as with 星期 xīngqī: 周一 zhōuyī "monday", 周二 zhōuèr "Tuesday"..., 上周 shàngzhōu "last week", 下周 xiàzhōu "next week". In this lesson, we see a new use:
我去中国旅游一周。 We will travel a week in China.
So what a difference between 周 and 星期? At the level of meaning, none. However, it should be noted that when 星期 will have a classifier, 周 will not have one:
两个星期 ⟷ 两周 two weeks
下个星期 ⟷ 下周 next week
Four characters word structure
Chinese people love the so-called four-character frozen expressions 成语 chéngyǔ "Chengyu". We saw in last lesson 成千上万 chéngqiānshàngwàn "thousands upon thousands". This is a vast subject that we will not discuss here. What must be remembered is that these four-character frozen expressions have a great influence on the spoken language and that Chinese like to construct expressions on this model. For example, in the text of this lesson you will find:
路窄车多 narrow streets and lots of vehicles
In good Mandarin Chinese we should write 路很窄，车很多 with 很 to remove comparison of an adjectival verb at the affirmative. But since we can simply make an expression in four characters, we ignore this grammar rule. You will see more and more of this expressions as you progress in Chinese. Do not be surprised, but try to assimilate them little by little.