问题补充：
This book will show the readers can be used in other contexts.
A. how that they have observed
B. that how they have observed
C. how what they have observed
D. that they have observed
答案：
A. how that they have observed
B. that how they have observed
(答案→)C. how what they have observed
D. that they have observed
解析：句意：这本书将向读者展示他们所观察到的东西怎样被用到上下文中。这里how引导的是宾语从句，在从句中what they have observed是主语，what在引导的主语从句中作宾语。that在名词性从句中不做成分，故排除；故选C。
