_______ 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.

This camera is of good quality. If it ______ break down within the first year, we would replace it with a new one.

If it _______tomorrow, I will go on a picnic.

____parents say and do has a life-long effect on their children.

It was funny that when _______ Mary began to weep sadly.