The stanza in Robert Frost's 'The Road Not Taken' that most supports the theme that sometimes human beings feel conflict because they cannot have everything they desire is STANZA 1, as it's the one that speaks of the sorrow he feels for not being able to take both roads. 
 
        
                    
             
        
        
        
Answer:  
The two sets of lines that are enjambed in this excerpt from John Milton's Paradise Lost are
Lines 3-4
Say first, for Heav'n hides nothing from thy view
Nor the deep Tract of Hell, say first what cause  
Mov'd our Grand Parents in that happy State,  
Lines 6-7
Favour'd of Heav'n so highly, to fall off
From their Creator, and transgress his Will  
For one restraint, Lords of the World besides?'
Explanation:
Enjambed lines are the ones that don't conclude the idea of the clause, it is instead continued in the next lines, where it may or may not conclude in case that it concludes it'll have a mark like a full stop or a comma if not it will be enjambed to the next line.