Question

This book will show you ___ can be used in other contexts.

A how you have observed B what you have observed
C that you have observed D how that you have observed
选哪个为什么？

Answer 1

选B
This book will show you what you have observed can be used in other contexts.
这句话的意思是：这本书将向你展示你观察到的东西如何在其他环境中使用

从句中的谓语observe是观察的意思，及物动词，必须跟宾语，但是它的后面没有宾语，所以连接词必须是能在从句中充当宾语的，how只能做状语，所以A和D都不对，至于that它在从句中不做成分，也不能选。这四个选项只有B的what可以在从句中做宾语，所以选B。