The correct option is SALES TRAINEES. In English language, parallel structures are used to show that two or more words are of equal in importance. In parallel structure construction, the structure and the tensed must match. In the sentence given above, you will observe that the subjects listed are all of the same categories with the exception of sales trainees. Sales trainees ought not to be there because sale trainee is not a course or subject that is taught in school. It refers to a person that is been trained to become a sale agent
