Which statement best explains the meaning of the oxymoron "joyful sorrow" as used in this quotation?

“My only child left for college today," said Mrs. Kim. "I felt a joyful sorrow as I watched him board the plane."

A)Mrs. Kim is happy her son is going to college but sad he won't be living at home anymore.
B)Mrs. Kim isn't completely happy about her son going to college because worrying about the plane flight makes her sad.
C)Mrs. Kim believes raising her son is the only joy she has in life, which causes her to resent him for leaving.
D)Mrs. Kim feels joy that her son is taking his first trip on a plane, but she also feels sad because he might be scared to be alone.