填空题
According to many scientists, solar energy will be used ______ (extend) in the 21 st century.
【正确答案】
1、答案extensively
【答案解析】[解析] 考点：词性转换。此处需要一个副词来修饰动词。其词形变化是：extend(动词)→4extensive(形容词)→extensively(副词)。
[例句] You should listen to the teacher carefully in class．
上课要认真听讲。