Greetings, What is the sign of past perfect tense? For example, in the sentence below, I think both options can be correct. A new hospital ............ in this town two years ago. a) had been built b) was built The active sentences could be: I had build a new hospital two years ago. I built a new hospital two years ago. But the key in the book is letter "b" (was built). I want to know how to distinguish "simple past" from "past perfect" in the passive sentences? Is there any special time adverbial for past perfect ? or) "The problem ............. by a few students." a) had been soved b) was solved which the active sentences can be: " A few students had solved the problem" and " A few students solved the problem".