Answer
Correct option is B that is Desktop computer
Step-by-step explanation
Option A
This option is not correct because in a Locomotive train steam, diesel or batteries are used.
Option B
It is Correct option because in desktop a transformer is there which uses AC current. Most of us have desktop and we used AC current to operate it we don't have any other option to operate a desktop except AC current
Option C
This is not correct option because in a car we used petrol, deisel, gas or DC batteries.
Option D
Option D is not correct option because to operate portable media player we can use both alternating current or batteries
Option
This is not correct option because in flashlight we uses DC batteries
Hope this answer will help you