______ a certain doubt among the people as to the practical value of the project.

When he knocked at the door, my mother was busy ____ supper.

If he takes on this work, he will have no choice but ______ an even greater challenge.＿

As an employee, I couldn’t help but ______ still for hours as the boss told me to.

---_________ she can’t find her keys? She’ll be locked out all night.---You are right. I’d better call her to check if she’s OK.