Are these sentences correct? b) He told me about many cities he had visited during his travelling. c) I couldn’t answer teacher`s questions because I hadn’t revised anything before the exam. d) When we came to the theater,the play had already started. e) I went to watch TV after I had written a letter to my friend. f) She couldn’t find a book I had lent her. g) She told me that she had worked in France and Germany. h) When I came to the car parking I realized that I had lost the keys. i) It was a firm I had never heard before, j) My headache disappeared after I had taken medicine. Are these sentences correct? I doubt about using Past perfect correctly here.