Перевести: моя сестра пишет письмо в это время. предложение приобразовать в отрицательное и вопросительное настоящего длительного времени.

My sister is writing a letter at the moment.
Is my sister writing a letter at the moment?
My sister isn't writing a letter at the moment.

My sister is writing a letter at the moment.
Is my sister writing a letter at the moment?
Yes, she is. She is writing a letter at the moment.
No she isn't. She isn't writing a letter at the moment.