"What are they doing?" 是表示 "他们去干嘛" 的英文短语。这个短语是由 "what"（什么）和 "are they doing"（他们在做什么）两个单词组合而成的。
例句：
What are they doing over there? 他们在那边干嘛？
I wonder what they are doing. 我想知道他们在干嘛。
Can you tell me what they are doing? 你能告诉我他们在干嘛吗？
翻译：
What are they doing over there? 他们在那边干嘛？
I wonder what they are doing. 我想知道他们在干嘛。
Can you tell me what they are doing? 你能告诉我他们在干嘛吗？