It is important to have your eyes examined regularly to check for any sign of eye disease that may not have any ________.
17. In China, _______ bicycle is ______ popular means of transportation.
18. --- What do you think of the furniture on exhibition? --- Well, great! But I don’t think much of _______ you bought.
19. The best job is _______ which uses your skills in doing something together with your interest in the subject.
20. In the past ten years, great changes _______ in my hometown.
21. The third and last chapter _______ by Professor Chen.