Betty will ring me up as soon as she _____ in Shanghai.
Chinese is one of ______ subjects in our school.
I was watching TV ______ my mother was writing an e-mail to her friend.
We must study hard so that we can get a good job when we ________.
David worked _______ a waiter in a restaurant in his part-time.
_______ she is in trouble, her friends will help her out.