I don't really understand why "which is" being used here. Can you give me some example sentences using "which is"?
Native speaker’s answer
Rebecca
"Which is" is used in this sentence as a pronoun in place of something that is not a person. It is placed at the beginning of a clause to provide extra information to something in a previous clause. Ex: That town, which is the town I used to live in, is growing rapidly. Ex: She claimed she wasn't there yesterday, which is a lie.