be almost done doing是什么时态和句型？

they were almost done building the new office tower but they hit a snag.

be almost done doing是什么时态和句型？ done与 be done的区别 to be done还是being done? all that can be done been done. being done, done ,to be done的区别 which cannot be done online. let it be done 是什么意思？？ all that can be done to be done的用法 Has all that can be done been done?