This has been bothering me, ever since I started learning English. It is concerning " 's " ; Which one is correct for the following examples ?
Car steering wheel or car's steering wheel
Door knob or door's knob
Computer screen or computer's screen
Dog house or dog's house,
Cell membrane (used in textbook) or cell's membrane
Road surface (used in textbook) or road's surface
Berlin streets or Berlin's streets
There are thousands of others, so I am looking for an "official rule".