I am showing my uncle（）our farm.They are cleaning the blackboard（）the back（）the classroomI can’t find my new book（）the shelfI am writing a letter（）my friends in America.The children are playing（）he playgroundA few students are running（）he playground.May I borrow an English book（）you.填介词或副词

I am showing my uncle（）our farm.They are cleaning the blackboard（）the back（）the classroom
I can’t find my new book（）the shelf
I am writing a letter（）my friends in America.
The children are playing（）he playground
A few students are running（）he playground.
May I borrow an English book（）you.填介词或副词