所谓的语文学习，主要是学习表达能力和理解能力。表达能力包括口语表达能力和书面表达能力，表达要求能够做到逻辑清晰，语言流畅准确。
语言学习的考核点由表达能力和修辞能力构成。接下来我就来具体学习一下表达篇的内容吧！
Essential and Nonessential Adjective Clauses
必要定于从句和不必要定语从句
Remember that an adjective clause is a dependent clause that acts like an adjective in the sentence. This means that it gives more information about a noun or pronoun in the sentence.
定语从句是一个从属分句，在句中作形容词。可以给出更多关于句中名词或代词的信息。
Sometimes the information given by the adjective clause is essential. An essential adjective clause is one that is needed for the sentence to make sense. If you took it out, you would not know all the information that you need to know.
有时，定于从句提供的信息至关重要。句中需要这一从句使句子的意思更完整。如果缺少此从句，就了解不到完整的信息。
At other times, the information given by the adjective clause is nonessential. A nonessential adjective clause is one that is not necessary. The sentence still makes sense and you know everything you need to know even without the clause. So, you could take it out.
有些时候，定语从句提供的信息不是那么重要。没有这一从句，句子也有意义，而且意思完整。因此可以删掉这一从句。
When a sentence has a nonessential adjective clause, the clause is set apart with commas. This shows that it is not essential.
如果一句中有不必要定语从句，就会用逗号把从句隔开，表示这句话并不是必须的。
Examples of Essential and Nonessential Adjective Clauses:
必要定语从句和不必要定语从句的例子：
Examples of essential adjective clauses:
必要定于从句的例子：
1) The man who left his wallet is coming back for it.
1）丢了钱包的男人又回来找钱包了。
It is essential for us to know which man.
有必要知道是哪个男人。
2) I do not remember the day that my cousin was born.
2）我不记得表弟是哪天出生了。
It is essential for us to know which man.
有必要知道是哪一天。
3) The time when I go to bed changes in the summer.
3）夏天的时候，我上床的时间跟其他季节不同。
It is essential for us to know what time.
需要知道什么时间。
4) I want the dog that is black and white.
4）我想要那只黑白相间的狗狗。
It is essential for us to know which dog.
我们需要知道是哪只狗。
5) Could you bring me the cup that is on the table?
5）可以拿给我桌上的杯子吗？
It is essential for us to know which cup.
我们需要知道是哪个杯子。
Examples of nonessential adjective clauses:
不必要定语从句的例子：
1) Lisa, who takes ballet with Jan, is my best friend.
1）和简一起跳芭蕾舞的丽萨是我最好的朋友。
It is not essential for us to know about the ballet.
不需要知道更多关于芭蕾舞的信息。
2) I won first prize, which was a blue ribbon.
2）我获得了一等奖，是条蓝色的丝带。
It is not essential for us to know the type of prize.
我们不需要知道是什么类型的奖。
3) My grandfather, who lives on a farm, said he would teach me to ride a horse.
3）我的祖父住在农场，说要教我骑马。
It is not essential for us to know where he lives.
我们不需要知道他住在哪。
4) The school library, which is next to the cafeteria, is my favorite place in the school!
4）咖啡馆旁边的图书馆是我最喜欢的地方。
It is not essential to know that it is next to the cafeteria.
我们不需要知道图书馆在咖啡馆旁边。
5) Mary, whose mom is a nurse, sits behind me in class.
5）妈妈是护士的玛丽，上课时坐在我旁边。
It is not essential for us to know what Mary's mom does.
没有必要知道玛丽的妈妈做什么。
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