For example, {HEAD ~ systems} can use {TAIL ~ feedstock materials}, such as cellulosic and lignocellulosic materials and starchy or sugary materials, to produce ethanol and butanol, e.g., by fermentation 
For example , { HEAD ~ systems } can use { TAIL ~ feedstock materials } , such as cellulosic and lignocellulosic materials and starchy or sugary materials , to produce ethanol and butanol , e.g. , by fermentation
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH