If you put down three choices, which you don't have to, then if you meet the requirements for each of those choices you will be assessed for each of them. After the assessment process you will be given a score for each occupation and if you have completed the eligibility requirements you will then be merit listed for those occupations with their scores. It is possible to be scored higher for your second choice or your third choice and you could be offered a position for either of your choices. Again just because there are three spaces does not mean you have to have three choices. If there is one or two particular trades that you are really interested in then only apply for them.