It is _____ to fly an airplane at three thousand miles an hour.
It is \_\_\_\__ to fly an airplane at three thousand miles an hour.
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Smith is to study medicine as soon as he _____ military service.
Smith is to study medicine as soon as he \_\_\_\__ military service.
Please be sure to telephone me the next time you _____.
Please be sure to telephone me the next time you \_\_\_\__.
Return the book immediately to the library as soon as you _____ with it.
Return the book immediately to the library as soon as you \_\_\_\__ with it.
You’ve already missed too many classes this term. You _____ two classes just last week.
You’ve already missed too many classes this term. You \_\_\_\__ two classes just last week.
There is a knock on the door. It is the second time someone _____ me this evening.
There is a knock on the door. It is the second time someone \_\_\_\__ me this evening.
—Is there anything wrong?—No, so far I _____ no trouble.
—Is there anything wrong?—No, so far I \_\_\_\__ no trouble.
This kind of glasses manufactured by experienced craftsmen _____ comfortably.
This kind of glasses manufactured by experienced craftsmen \_\_\_\__ comfortably.
—What do you think of the TV play?—Wonderful. It is worth _____ a second time.
—What do you think of the TV play?—Wonderful. It is worth \_\_\_\__ a second time.
_____ today, he would get there by Friday.
\_\_\_\__ today, he would get there by Friday.