"Behind the door, there is a boy" 可以用英语表示为 "There is a boy behind the door"。
这句话的结构是："there is/there are" + 名词 + "behind/in front of/next to" + 地点名词。
例如：
There is a cat behind the couch. (沙发后面有一只猫)
There are three cars in front of the house. (房子前面有三辆车)
There are several books next to the bed. (床旁边有几本书)
"There is/there are"是英语中表示存在的常用短语，"behind/in front of/next to"是表示位置关系的副词。