{TAIL ~ at least one pair} of {HEAD ~ wheel driving means} adapted to be driven independently of each other 
{ TAIL ~ at least one pair } of { HEAD ~ wheel driving means } adapted to be driven independently of each other
TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH