_ difficult and challenging the task may be, wemust finish it on time, because there is a possibility _______our work will godown in history.

It is reported that a large number of people _____ been killed and the number ____ added up tonearly 70,000[ ]

___ help, one says "Thankyou" while when _____ help, one asks "Can I help you"

Mo Yan won the 2012 Nobel Prize in Literature, he still lives a simple and quiet life.

________ many times，I stilldidn’t know how to operate the machine.