Help: "order of preference" on Form-Schedule 3: Economic Classes

[zhaotianwu]

On Form-Schedule 3: Economic Classes, the last question (number 12) asks you to fill in your preference of work experience to be evaluated.
If I had only one job, e.g. a computer manager, can I put in several job titles and NOC numbers for that one job and let Visa Officer determine which one he/she thinks fit? Or I must only choose the most appropriate one for that one job and only if I worked several different jobs can I fill in with different job titles?
To me this question is very vague, so I want some peer helps from our buddies here! Thanks.