The tourists, had enjoyed themselves so much in the botanic garden, were worn outA. all o

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A. all of what
B. all of which
C. all of them
(答案→)D. all of whom
解析：句意：在植物园玩得很高兴的所有的游客都精疲力竭了。这里使用了定语从句，先行词是the tourists，定语从句是由代词all+介词of+关系代词引导的，因为先行词是人，所以关系代词用whom，选D。