1．They each had their own language and Anglo-Saxon(the base of old English) developed from mixing these languages with Celtic.  他们都有自己的语言，盎格鲁—撒克逊语（古英语的基础）是把这些语言与凯尔特语相结合并发展起来的。
这是一个由and连接的并列复合句，其中的介词短语from mixing these languages with Celtic在第二个分句中作方式状语。develop from意思为“由……发展而来”，mix… with 则表示“使……与……结合”。
Land animals are thought to have developed from sea animals.
陆地动物被认为是从海洋动物进化而来的。
The flowers developed from those that once grew in the forest.
这些花是从原来长在森林里的花发展而来的。
He never mixes his business with his private feelings.
他从不在工作中掺入私人感情。

2．So, the words we use for most animals raised for food, such as ox, cow, sheep and pig, come from old English, while the words for the meat people eat come from French: beef, mutton, pork and bacon. 所以，表示饲养食用动物，如公牛，母牛，羊和猪时，我们使用了古英语的单词；而像牛肉，羊肉，猪肉和熏猪肉这些人们吃的肉类的单词却源于法语。
这是一个由while引导的并列复合句。第一个分句是一个含有定语从句的复合句。主句为 “the words come from old English”， “we used for most animals raised for food”是定语从句，过去分词短语raised for food 充当定语，修饰 most animals。such as意思为“例如”，常用于多项列举。句中while为连词，表示转折或对比，意思是“然而”。   
Terrorist attacks have broken out in quite a few countries, such as the USA, Britain and Spain.  
恐怖袭击已在好多国家发生了，例如，美国，英国和西班牙。
Boys like sports, while girls like dancing.
男孩子喜欢运动，而女孩子则喜欢唱歌。

3. The Chinese language differs from many western languages in that it uses characters which have meanings and can stand alone as words. 中国语言与西方语言不同，是因为中国语言使用了方块字，方块字本身有词义，而且可以单独组词。
这是一个主从复合句。 “in that it uses characters which have meanings and can stand alone as words”在句中充当原因状语从句。in that可以用because替换，意思是“因为”。differ from…意思为“和……不同”；stand alone意思是“单独；卓越”。例如：
I was lucky in that I was able to find a job in Shanghai.
我很幸运是因为我在上海找到了一份工作。 
Chinese customs differ greatly from those of the west.
中国的风俗习惯和西方国家的风俗习惯大不相同。
He stands alone among his classmates.
他同班同学中没有人能和他相比。