Поставь вопрос к выделенным словам:
There are two pens on the table.
There is a carpet on the floor.
There are ten trees in the garden.
There is a blackboardin the classroom

Are there two pens on the table?
Is there a carpet on the floor?
Are there ten trees in the garden?
Is there a blackboard in the classroom?
Все просто. Только глагол be (I, you, we, he, she, it...) в начало поставить надо.