It would be D as the symptom would be vision. Difficultly sleeping would be a neurological related condition along with sinus headaches. Failing grades wouldn't generally warrant a trip to the doctor while the symptom of eye squinting would be directly vision.
It's very easy for things to go awry when there is nothing documenting the agreement between the parties or variations to that agreement. That's why it's important to ensure that any agreement you have, whether with an employee, supplier, customer or business partner, is captured in writing and any variations to the original agreement are also documented, approved and signed off
