His father feels ___ his duty to help others.
She bought the same skirt at a lower price at the same shop where I bought mine because she was a __________ customer.
China is one of the developing countries ________ the third world.
—How long ________ at this job?—Since 1990.
According to today’s newspaper, the escaped prisoner threatened to _____ the police station in the near future.
Mary heard ____strange sound at ____midnight outside her house and got scared.