Editor
You are testing a hypothesis; "students learn more if They drink tea before sitting to study". Your 20 experimental students drink tea before studying; you test their learning by giving questions. Your 20 students in the control group should have all experimental conditions identical to the experimental group EXCEPT that; 
Difficulty: Hard
A: 

They should take tea with more milk and sugar 

B: 

They should take tea before as well as during study 

C: 

They should not take tea before studying 

D: 

They should not sit for studying

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