He was about to leave the office for home _______someone knocked the door and asked for some help.
Nuclear radiation is said __________ the biggest health challenge in Japanese Earthquake over the past few months.
Tom’s English is not good, so he devoted all his free time to __________ it.
To his surprise, Jack found his son _______as Santa Claus on Christmas Eve.
______ his expression, he didn’t _____the driving test.
The man kept silent in the room unless_______.