题目内容：
Whatdoestheauthorthinkofbiofuels?
A．TheykeepAmerica'seconomyrunninghealthily． B．Theyprovetobeagoodalternativetopetroleum．
C．Theydonotprovideasustainableenergysupply．
D．Theycauseseriousdamagetotheenvironment
参考答案：
答案解析：