I didn't see your sister at the party. If she __, she would have met my brother.
At the railway station,the mother waved goodbye to her daughter until the train was________.
________by a group of children,the old man was delighted.
Learning English means _________ memorizing a huge lot of words.It involves a large amount of reading as well.
Tom as well as two of his classmates _____ invited to the party.
The fact has worried many scientists ______ the earth is becoming warmer and warmer these years.