执行下面Python代码后，输出的结果是？（ ）
1 users = [
2 {"name": "Tom", "skills": {"Python", "Java", "C++"}},
3 {"name": "Join", "skills": {"Python", "Java"}},
4 {"name": "Gaia", "skills": {"Java", "C++", "SQL"}}
5 ]
6
7 skills_sets = (user['skills'] for user in users)
8 common_skills = set.intersection(*skills_sets)
9 print(common_skills)