Present Simple.
The teacher gives the task to the student .
The teacher doesn`t give the task to the student .
Does the teacher give the task to the student? Yes, she does.
Past Simple.
The teacher gave the task to the student .
The teacher didn`t give the task to the student .
Did the teacher give the task to the student? Yes, she did.
Present Simple.
Your sister is at school.
Your sister isn`t at school.
Is our sister at school? Yes, she is.
Past Simple.
Your sister was at school.
Your sister wasn`t at school.
Was our sister at school? Yes, she was.