As is known to all language learners, the newly learnt words will soon be forgotten unless they are _______ used in everyday communication.
Not until all the fish died in the river ________ how serious the pollution was.
His first book ______ last month is based on a true story.
________by curiosity,he opened his wife’s notebook and began reading her diary.
________ the delayed flight will take off depends much on the weather.
I________ along the street looking for a place to park when the accident________.