Had: v. yes; Hold; Possession; Composed of; To display (attributes, features).

Bee: sue once; Have been to (a place).

Finish: end; End; End; Cooked; Cooked; Conform to etiquette; Comply with the rules; Decent. She knew it was difficult to undo the damage that had been done.

She knew it was difficult to undo the damage that had been done.

The work was not done thoroughly.

This work is not done very seriously.

Make time to discuss what has been done.

Make time to talk about what you have done.

Therefore, we conducted three studies to explore the above problems.

Therefore, this paper discusses the above problems through three studies.

By the end of last month, all the work had been finished.

By the end of last month, all the work had been finished.