I'm staying for two days
RIGHT
They've known each other for 3 months
RIGHT
They're staying with us since Christmas
WRONG. They've been staying with us since Christmas
She's been wanting to tell me ever since we first met
RIGHT
How long have you been in England for?
RIGHT
He's lived in Australia since 8 years
WRONG. He's lived in Australia for 8 years
I am here since Monday
WRONG. I've been here since Monday
I haven't yet seen him
WRONG. I haven't seen him yet
He hasn't still come
WRONG. He hasn't come yet
What've you been doing with yourself these last few months?
CORRECT
They are together three years now
WRONG. They've been together for three years now
She hasn't written for ages
RIGHT
He's arrived last week
WRONG. He arrived last week
They've lived in the same flat 6 years ago
WRONG. They've lived in the same flat for 6 years
She worked at IBM for 15 years
WRONG. She's worked at IBM for 15 years