A course might be missing for one of the following reasons. If you transferred from another Faculty or School the course may not be accepted in an Arts and Science Program. If you are in a Major-Minor Plan combination the issue may be overlap. A course used as Core or Option in the Major Plan may not also be used as Core or Option in the Minor Plan.
If you believe a course is missing in error, please consult with your department or Student Services. It is possible departmental consent is required to permit you to use the course, or a course from another Faculty/School needs to be approved, or a course has gone to the wrong requirement and needs to be directed to the appropriate one. These situations can be handled with a student exception.