When she ____________ the car door, she realized she had left the key in her bedroom.
It will take a long time for the effective use of natural resources _________.
_________ hard one may work, one cannot master a foreign language in a year or two.
That is just _________ challenging job all the workers want to get. Do you have anyone in _________ mind for it?
--Jack! I have left my key to the office at home. -- Don’t worry. I _________ it for you. Wait a minute.
--Did Mary return late last night? --No. It was not yet 7 o’clock _________ she arrived home.