书名：国际学村 新多益阅读题库大全
页数：p.53 第18题
题目：
There has been so little information on some health concerns that it
is diffcult for the individual to decide whether or not he should see
a doctor.
疑问：
解答写"so little information"是实际主词，
依照前面文法说明，实际主词是由“不定词”或“that子句”组成的，
那想请问为什么"that it is diffcult..."不是实际主词呢？