干密度=（）/环刀体积。
A.干土质量
B.湿土质量
C.环刀+湿土质量
D.铝杯+干土重质量
参考答案：A
Ted told his father he ______ his homework three hours before.
A．finished
B．has finished
C．was finishing
D．had finished
试比较xDSL、HFC以及FTTx接入技术的优缺点？
