Need some help with the prepositions AT and BY...
AT: used to say exactly where something or someone is, or where something happens
BY: beside or near something.
1. She stood AT the window
2. She stood BY the window
3. Who is AT the door?
4. Who is BY the door?
5. I left him AT the sledge
6. I left him BY the sledge
7. He was standing AT the bed.
8. He was standing BY the bed.
Is AT/BY interchangable in this context? If not, what are the differences?
And if only one of them is right, why is it so?
Cheers
Lanta