Cannot add Physics C: Mechanics in the courses section

Hi,

I would like to start AP Physics C: Mechanics and it seems like Khan Academy already has a course at https://www.khanacademy.org/science/ap-physics-c-mechanics  . However, when I try to add this course with 'Add another course' button on courses section it does not show the course. Only Physics 1 and Physics 2 seems to be there even though I expand the science section.