The past perfect continuous

The past simple refers to a specific completed event in the past. The past perfect continuous describes a repeated action or continuing activity that was taking place bebore taht completed event.

1. He had been studying english for two years before he went to London.
2. By the time katie arrived home, she had been driving for six hours.

how to form

subject + had been + verb + ing + rest of sentence.

the present perfect continuous and the past perfect continuous

The present perfect continuous is used to talk about an action in progress or repeated activity that taking place until the present moment.

I'm really thirsty. I have been cycling for two hours.

The past perfect continuous is used to talk about an ongoing action or repeated activity that was taking place until another speified moment in the past.

I was really thirsty. I had been cycling for two hours.