When _________ our national flag _______, we feel our hearts full of pride and strength.
—What was it that caused the party to be put off? —________ the invitations.
Who ________ that played a trick on the new English teacher?
—Where did you pick up the stamp? —It was at the post office ________ we worked in the summer vacation.
—Was it by cutting down staff ________ she saved the firm? —No,it was by improving work efficiency.
Is it that you often play computer games ________ worries your parents?