Ответы и объяснения

1.I had bought that flat by last year.(presnt perfect)/I bought that flat last year.(past simple)
2.Mary had left her bag before she went to the cinema./Mary left her bag,and she went to the cinema.
3.My teacher had taken the test to us before the lesson was over./My teacher took the test to us,but the lesson wasn't over yet.
4.Had you been in Scotland by the end of last month?/Have you ever been in Scotland?
5.He had helped his mother before he passed his exams./He helped his mother,but then he passed his exams.