I wonder why you didn’t do as ________ and it’s the third time you have done this. 

So difficult _______it to work out the problem that I decided to ask Tom for some advice.

Hearing the dog barking fiercely, away _____. 

The bus hit against a tree in the fog and __________ to the deep valley, with then passengers killed and twenty wounded.

—It is said that we will have another examination next week.—Really? ________, we must begin to prepare right now.