1gim present perfect - prośba o sprawdzenie

Witam. Czy mógłby mi ktoś sprawdzić, czy te zdania są poprawnie napisane? Byłabym bardzo wdzięczna.
1. I've known Richard since we were at school together.
2. Since Alex has arrived in this country he made a lot of friends.
3. The car hasn't broken down since I got it.
4. I haven't seen Jenny since we went to the cinema last month.
6. Since we had an anrgument last year she hasn't spoken to me.

Z góry dziękuję
Pozdrawiam
Dominika

>1. I've known Richard since we were at school together. OK, lub ...since we've been at school together.
>2. Since Alex {} arrived in this country, he {has} made a lot of friends.
>3. The car hasn't broken down since I got it. OK
>4. I haven't seen Jenny since we went to the cinema last month. OK
>6. Since we had an argument last year, she hasn't spoken to me. OK

Bardzo dziękuję :):) I jeszcze jedno mi umknęło.. czy
"How long has your dad had this car ? " jest poprawnie?

jest :)

Jeszcze raz bardzo dziękuję ;D