His aunt’s letters ___of those beautiful days when they used to live together in his hometown.
If human beings had been a bit less greedy and cruel, more birds and animals _______dying out.
With a lot of difficult problems____________, the manager felt worried all the time.
--Was Tom there when you arrived? --Yes, but he___________ home soon afterwards.
—Look at these tracks. It __________ be a wolf. —It needn't be. It ___________ be a fox.
Travelers_______________ that they should bring their ID cards with them.