__________ a certain doubt among the workers as to the necessity of the work.
We've had a good start, but next, more work needs __________ to achieve the final success.
Passengers are permitted __________ only one piece of hand luggage onto the plane.
Having finished her project, she was invited by the school __________ to the new students.
Bill suggested __________ a meeting on what to do for the Shanghai Expo during the vacation.
Susan wanted to be independent of her parents. She tried __________ alone, but she didn't like it and moved back home.