I am ISSA Certified, so I had different examinations. Some of them can be quite hard and difficult to understand. Regardless, this picture is a bad one, in that their model is wearing BLACK SHORTS on a BLACK SEAT of the machine. He should be wearing something brighter to distinguish what you're looking for.
With that said - and I may be totally wrong here, so take it with a grain of salt - I'd have to say either B or D.
B. His Hip Complex is flexing, but his glutes and that region seem to be coming off of the machine to complete the repetition
C. We hear about Anterior Pelvic Tilt often, but never Posterior Pelvic Tilt (but it is a thing). With this picture it looks like his Hip complex is tilting in a posterior fashion too much, but I've never heard of it when using a Leg Press or anything...
Overall, weird question in which the answers for both B & C are quite similar. But I am assuming this is a multiple choice examination, so getting one wrong shouldn't be the end of the world.
Best of luck!