Impromptu is an unrehearsed speech. Not rehearsing would not allow speakers to gather 100% of their thoughts.
        
             
        
        
        
Hey there!
a continent is like a member of a band because they both come together to make something great (the continets make earth and the band makes music)
an ocean is like a lion because they both are very powerful and many people are scared of them both.
i hope this helps a bit :)
        
             
        
        
        
This is the correct form, though you need to be specific and describe who "them" is.