I'm in a class that requires clinical problem solving skills and team based learning. I'm the leader of my group, and my group is pretty smart and hard working. I'm also decent at planning and delegating tasks. The problem is that I have to constantly repeat myself in order to get some people to listen. I'm not tall and my voice isn't low and commanding. I am, however, in good physical shape. One group member also corrects me in a very sarcastic manner when I make a mistake once in a while. I don't respond emotionally, but I want more advice than just "don't be emotional." How do I develop a more commanding presence, and what is the best way to deal with challenging and sarcastic remarks from people? I realize this isn't exactly sexual strategy, but It seems related to it.