The correct answer is A. We practiced for the debate and many arguments were rehearsed.
As you can see in this sentence, in the first part the pronoun <em>we </em>is used, and in the latter part, that pronoun just disappears and the sentence suddenly becomes passive rather than active. The shift isn't done properly - it is rather awkward. The other options are consistent - they use only one voice rather than two (like in sentence A). 
 
        
             
        
        
        
The argument relies on claims that are not backed up by facts
 
        
                    
             
        
        
        
Spent is the most negative connotation.
Explanation:
 Fatigued is to feel exauhsted.
 Weary is lack of sleep, tiredness.
 Tired is just a minimal drousy feeling. 
And spent is as if your energy was all used up, consumed.
 
        
                    
             
        
        
        
Explanation:
Because it doesn't live under a rock... It melts from one. (mountains)
 
        
                    
             
        
        
        
It seems that you have already filled the correct pronoun in the blank provided. Yes, the correct answer to complete this sentence is the pronoun "this". The pronoun "this" is an example of a demonstrative pronoun. Other demonstrative pronouns also include these, those, and that. Hope this answer helps.