те Надо вставить in,on,at
3. Did you hear the doorbell? There is somebodythe door.
4. She is doing her homeworkher desk

3. at

4. on

Объяснение:

Надеюсь это правильно, если не так то пршу прощение.

3. Did you hear the doorbell? There is somebody on the door

4.She is doing her homework on her desk

ТУТ ВСЕ ПРАВИЛЬНО