1. Internet 只有一個，永遠(yuǎn)要用the
Network N. countable
Life- lives plural
E.g. In this day and age, according to the development of the internet, social networks have become more and more vital in our lives.
2. It 只用于前面的某個主體，若前句主體不明或太長，用this
E.g. In this essay, I will discuss whether this is positive or negative.
3. Have been
e.g. Since I have been in Australia, I have made a lots of friends.
