There is one registered course that I would like to drop.
"There is one registered course"＝「一つと履修登録した科目があります」
"that I would like to drop"＝「取り消したいのが」
Sentence in context:
"I realized that I would be too busy if I try to take all the courses I signed up for this semester, so I would like to drop one of them."
アメリカ合衆国 
