'which' is a determiner pronoun asking for information specifying one or more people or things from a definite set. It is the suitable word to use in the sentence.
'Who' is a subject pronoun that is used to describe who performed an action or who is in a specific state. 'Whom' is an object pronoun that refers to the person who was the recipient of an action. 'Whose' is a possessive pronoun that refers to the person to whom something belongs.
You are . . . . . . . . your time trying to persuade him, he will never help you.
In the above sentence, we used past perfect continuous tense with the action verbs to talk about some repeated actions that occurred in the past.
The past perfect progressive tense, is also called past perfect continuous tense. We use past perfect progressive tense to express some event that had already happened and continued it with some other point in the past.
By using, had been + the verb's present participle( + ing) we frame the sentence.
We use little with uncountable nouns. We use few with plural countable nouns.
They are used in formal contexts:
I’m not very happy about it but I suppose I have little choice.
Few cities anywhere in Europe can match the cultural richness of Berlin.
I rode my bike, . . . . . . . . has a headlight, home in the dark.