Fuel were present at the sites. As a fuel, wood has remained in use up until the present day, although it has been superseded for many purposes by other sources. Wood has an energy density of 10–20 MJ/kg. Recently biofuels have been developed for use in automotive transport (for example Bioethanol and Biodiesel), but there is widespread public debate about how carbon efficient these fuels are. Fossil fuels are hydrocarbons, primarily coal and petroleum (liquid petroleum or natural gas), formed from the fossilized remains of ancient plants and animals by exposure to high heat and pressure in the absence of oxygen
Interlanguage fossilization does motivation to achieve native-like competence diminish? The concept of fossilization in SLA research is so intrinsically related to interlanguage that Selinker considers it to be a fundamental phenomenon of all SLA and not just to adult learners. Fossilization has received such wide recognition that it has been entered in the "Random House Dictionary of the English Language" (1987). Selinker's concept of fossilization is similar to that of Nemser, Tarone, and Sridhar, all of whom attempted to explore the causes of fossilization in second language learners' interlanguage. Fossilization has attracted considerable interest among researchers and has engendered significant differences of