They have been waiting for many hours to see the singer, but the airplane must have been _____.

—Look!He’s running so fast!—Hard to _______ his legs were once broken.

We are at your service. Don’t _____to turn to us if you have any further problems.

Don’t be so discouraged. If you       such feeling, you will do better next time.

As is known to all,the water in the sea______much salt.