word choice - たたく versus ぶつ in a JLPT question

In my JLPT practise book, there is a section demonstrating the difference between なぐる, たたく, 打{う}つ, and ぶつ. If I understand them, they are all variants of "hit", with subtle nuances to differentiate them.

I have this example explaining the use of ぶつ:

いたずらをした子供{こども}は、母親{ははおや}にお尻{しり}をぶたれた。

And then I have this question:

なまけ者{もの}の弟{おとうと}は人{ひと}から尻{しり}を_____ないと、なかなか仕事{しごと}をしない。

A　ぶたれ 　B　たたかれ 　C　打{う}たれ 　D　なぐられ

I chose A, which means I fell unto the usual JLPT trap where they deliberately mislead with similar contexts. D'oh!

Still, in any case, I can't see why B is a better answer.　In fact, the subtleties of difference make me unsure why any of them are not appropriate.

What makes B the right answer, and the rest wrong?

Answer

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  尻をぶつ:

  
  

  
  

  Means to spank someone as punishment for something which has been done (in the first case because of naughtiness.)

  
  

  
  


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  尻をたたく:

  
  

  
  

  Means to give someone a good hiding without those connotations (in that case because of laziness.)

  
  
  

  
  


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  打つ:

  
  

  
  

  Doesn't work because ぶつ is used for people and 打つ for inanimate things.

  
  

  
  


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  殴る:

  
  
  

  
  

  Doesn't work because it's more for violently hitting/continuous beating of someone with a stick/fist etc.

  
  

  
  

なまけ者 means "lazy person" and なかなか仕事をしない means "the (younger brother) stays lazy" in this context I believe, so the sentence would translate to "unless the lazy younger brother is given a good hiding, he stays lazy."