In the language of the computer profession, one thousand position of main storage is represented with the letter

The correct answer is: K.

In the language of the computer profession, one thousand position of main storage is represented with the letter K. This is because the letter K is used to represent the kilobyte, which is equal to 1024 bytes.

The other options are incorrect because they do not represent a valid unit of measurement for computer storage. The letter L is used to represent the light year, which is a unit of astronomical distance. The letter M is used to represent the megabyte, which is equal to 1024 kilobytes. The letter C is used to represent the Celsius scale, which is a scale for measuring temperature. The letter E is not a valid unit of measurement for computer storage.