The scientist knew nothing about the matter, because he was always _________ himself in his study.
______ we gave him something to eat, he would save it up for his little sister.
--All students must hand in your exercises right now.-______ We don’t have enough time to finish them.
Smoking is one of the ______ cause of cancer, killing millions of people each year.
______ his father’s letter, he decided to make a call to him.
Last week, Susan and David, ______ our university’s student association, met the Chinese guests at the New York airport.