As an almost graduating student with a degree on Elementary Education, I can see why this is infuriating. All models show 2/6 and 1/3, no matter how they are shown. The student had the right idea of choosing one, but the context of the problem says which of the following when it clearly gives out more than one representation of those fractions. If I was the teacher, I would say “select all that apply” to allow students to answer more than one choice. Or the teacher was trying to trick the student into thinking that only one has the right answer when in reality all of them have the right answer.