_______ the smoke come out of the building, my first thought was to call the fire department as soon as possible. 

—You look unhappy， my son?—I’m wondering how long it’ll be          we come to China again.

 —Isn’t it time you _______ down to _______ your own things? —I’m sorry for the delay, Dad.

______ Marx's works with Engels', and you'll find many differences．

Mike has much difficulty ________ Chinese so he often asks me ________ help.

You can hardly imagine what great difficulty we had _________ the task.

Rather than _________ on a crowded bus, he always prefers _________ a bicycle.

It is no good ______ him. He doesn’t help himself.

This is the first time that I        it.

— Why haven’t you asked her to come here?— She _______ an important experiment when I found her and she _______ it.

_______ good use of learning resources such as the website and library, and you will make great progress.

How long do you think ____ the car factory launches a new model?

I used to go camping a lot, so it isn’t the first time I ____in a tent.

 I had just got up and was about to cook my breakfast ___the telephone rang loudly, but it hung up __I could answer it .

____the book if you are free, and you will learn a lot about how to study English .

—Are you going there with us? —If Mary wants to go, ______.

This is the first time that I      face to face with the president.

How time flies! It has been ten years         I moved to Chongqing.

The mother along with her children _______  in the supermarket when the explosion happened.

It was the first time that little Tony ____ a speech in front of so many people.