首先我们来看下it is、since和before的大致意思:
it is:词性为短语,it is是由it和is组成的短语,it代表无生命的物体或不明确的主语,is是be动词的第三人称单数形式。
since:词性为介词,since是一个基本介词,表示从某个特定时间开始,引导一个时间点、时间段或事件
before:词性为介词,before是一个基本介词,表示在某个时间点之前发生的事情
通过下面的表格我们了解下it is、since和before的含义、发音和用法
接下来让我们看下it is、since和before的用法区别:
1.含义:it is since强调从过去到现在的时间段,而it is before则强调在某个时间点之前
例子:
- It is three years since I graduated from university.
(It is three years since I graduated from university.)
- He left the house five minutes before I arrived.
(He left the house five minutes before I arrived.)
2.用法:it is since用于表示从过去到现在的时间段,而it is before用于表示某个时间点之前的动作
例子:
- It is two weeks since I last saw him.
(It is two weeks since I last saw him.)
- We should arrive at the airport two hours before the flight.
(We should arrive at the airport two hours before the flight.)
3.位置:it is since位于句子的开头,而it is before位于句子的中间或结尾
例子:
- Since I moved to this city, I have made many new friends.
(Since I moved to this city, I have made many new friends.)
- I should finish the report before the deadline.
(I should finish the report before the deadline.)
4.时间点:it is since后面跟的是起始时间点,而it is before后面跟的是结束时间点
例子:
- It is three o'clock since I last ate.
(It is three o'clock since I last ate.)
- You need to submit the application before June 1st.
(You need to submit the application before June 1st.)
5.动作延续:it is since强调动作从过去一直持续到现在,而it is before则只强调发生在某个时间点之前
例子:
- It is two years since I started learning piano.
(It is two years since I started learning piano.)
- They finished their homework before dinner.
(They finished their homework before dinner.)