The mixture of his improved self-confidence and never-ending efforts is ________ lies behind his rapid progress in his study.
—Come on, please give me some ideas about the project.—Sorry. With so much work __________ my mind, I almost break down.
— Robert is indeed a wise man.— Oh, yes. How often I have regretted __________ his advice!
Leonardo da Vinci(1452-1519)__________ birds kept in cages in order to have the pleasure of setting them free.
The children talked so loudly at dinner table that I had to struggle __________.
—The last one __________ pays the meal.—Agreed!