同学你好，该知识点来自沪江网校《【Uni智能】大学水平进阶托福105分【北美全能畅学班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好，
What worried the child most was ____ to visit his mother in the hospital
由于空格前面是was即位于，所以可知我们需要补充的是宾语部分即需要名词或名词形式的词组
根据句意可得，应该是他不被允许去医院看他的妈妈
his和后面的not being allowed作为一个动名词组来表示原句为 What worried the child most was that he was not allowed to visit his mother in hospital.

希望有所帮助！