16.But for your help, I couldn’t have passed the exam. Had ___________________________________________. 17. “When will you come back, Nga?” I asked ___________________________________________. 18.No one has bought this house. This house ___________________________________________. 19.She didn't take an umbrella so she got wet. She wouldn't ___________________________________________. 20.It was a mistake for him to buy that house. He shouldn’t _________________________________________.