All the elder people ______ at the party were those _____involved in (参与)community service.
It was not until she had arrived home _______ her appointment with the doctor.
Smoking, ______ is a bad habit, is popular with the young.
The number of the people who own cars ______since 1990.
— Is he coming? — ______. He may not have time.
It took him a long time to ______ the skills he needed to become an artist.