Answer:
The best answer is A historian who claims the Boxer Rebellion followed directly from the actions of external colonial powers.
In order to understand this question, let us investigate what counterclaim means. It means a claim made to invalidate a previous claim. In this context, our answer needs to have, in its context a structure that goes against what the first historian said.
A historian who claims the Boxer Rebellion followed directly from the actions of external colonial powers - True - By giving a total antagonist cause for the rebellion, a cause that sustains itself with no connection to the previous argument, this case qualifies as a counterclaim for the first historian.
B. A historian who shares a diary entry from a Chinese woman who lost her crops to drought - False - This argument contributes to the original argument, showing a case that supports the historian.
C. A historian who offers evidence that Christians were targeted during the Boxer Rebellion - False - This claim only indicates the possible targets of the Boxer Rebellion, knowing the first claim is about the reason for the rebellion, it does not qualify as a counterclaim.
D. A historian who shows that harvest yields declined in the years before the Boxer Rebellion - False - This argument reinforces the first historian argument, showing one possible cause for the massive drought and famine in China.