People are starting to use energy from the sun, wind and water because they cost very ________ and will never ________.
A:few; run out
B:low; be run out
C:much; be run out
D:little; run out
在比例尺为1:10000的地图上,有甲、乙两个相似三角形区域,其周长分别为10cm和15cm.
下列各式中,计算结果为a6的是( )