某人
It is _____ to fly an airplane at three thousand miles an hour.
It is \_\_\_\__ to fly an airplane at three thousand miles an hour.
We must have an engineer _____ the workers build the house.
We must have an engineer \_\_\_\__ the workers build the house.
Please pass me the dictionary _____ cover is black.
Please pass me the dictionary \_\_\_\__ cover is black.