1,You should see the dentist, said Mai

-> Mai advised that i should see the dentist.

2,I spent seven years at secondary school and then I went to university

---> After having  spent  seven  years  at  secondary  school  I  went  to  university.

3, people say that the car driver was driving very fast at the time of the crash

-->The car driver is said to drive very fast at the time of the crash.

4,My grandfather built this house 20 years ago

--> This house was built by my grandfather 20 years ago.

5,I regret not buying any tickets for the correct

-> I wish I had bought tickets for the correct.

$1$. Mai advised that you should see the dentist

$2$. After I had spent seven years at Secondary school, I went to university

$3$. The car driver is said to have driven very fast at the time of the crash

$4$. This house was built by my grandfather 20 years ago

$5$. I wish I had bought some tickets for the concert