Some researchers believe that there is no doubt______a cure for AIDS will be found.

_______ difficult and challenging the task may be, we must finish it on time, because there is a possibility _______our work will go down in history.

Why don’t you use the knife—It needs ___________________.

________，I managed to get through the game and the pain was worth it in the end.

(2011·江西)It ________ be the postman at the door.It’s only six o’clock.