1.youhavenoideahowbusywewerethesedays为什么how前不加that
1.allthemachineshadfinishedbytheendofthefollowingweek为什么要用hadfinished不能用finishes吗,怎么看2.2.sincetheearthisround,whydowenotfalloff的since为什么不能换成as3.Bbelong有进行时态,有加ing吗