Ответ: there is a book on the desk.

There are pencils in the pencil case.

There is a teacher in the classroom.

There are 20 classrooms in the school.

There are 2 houses in the street.

Объяснение: пиши are во множественном числе и is в единственном:

There is a house in the street.( a house - единственное число)

There are 10 houses in the street.(houses - множественное число)

Удачи в учебе!