поставьте предложения в вопросительную и отрицательную форму:
1. Her sister studies at school.
2. We always meet him on Mondays.
3. He is a doctor.

1.      
Her
sister studies at school.

Does her sister study at school?

Her sister doesn`t study at school.

2.      
We
always meet him on Mondays.

Do we always meet him on Mondays?

We always don`t meet him on Mondays.

3.      
He
is a doctor.

Is he a doctor?

He isn`t a doctor.