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.