TPO8听力关于vision correction的问题

irisgycUID: 2683186

3.      What does the professor imply about theinvention of eyeglass?
A.    Its historical records are more detailedthan those of other inventions
B.     It has little impact on social attitudestoward vision correction
C.     Its occurrence in different places atapproximately the same time is out unusual
D.    It contributed to a substantial increase inthe number of literate people.
这道题我错选了D。看解析上说C选项out unusual就是不寻常的意思，但是原文有这样一句话：Independent discovery means when something is invented in different parts of the world at the same time and it's not as unusual as it sounds. 这句话是说独立发明not unusual吗？
百思不得其解啊:confused:
谢谢各位~~~

牧野2013UID: 3405435

我也是对out unusual的意思有疑问，在网上还是没有找到满意的答案，能有哪位考友解答一下吗？是TPO8中Lecture 3 History那篇。