There is a key and a book. 这句话没有问题.
解释：there be 句型,若句子中有几个并列的主语时,be的形式要与离其最近的一个主语在人称和数上保持一致.如:
There is a boy, a girl and two women in the house.
房子里有一个男孩,一个女孩和两个妇女.
There are ten students and a teacher in the office.
办公室里有十个学生和一个教师.
祝您学习进步,更上一层楼!如果答案您满意,请记得采纳,谢谢!O(∩_∩)O