已知△ABC∽△DEF,若△ABC与△DEF的面积的比为4:9,则△ABC与△DEF周长的比为____
When does Mike usually go to school?
2×( )<15____
( )×7<36____
( )×7<22____
6×( )<43____
关于能源的利用,下列有关说法正确的是( )