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18. A. e-books (It is convenient to read e-books when you travel.) 19. C. portable (Earbuds are small, light, and portable.) 20. B. save (Washing machine or vacuum cleaner can help you save time while doing housework.) 21. C. playing (My computer is used for playing music and video.) 22. C. to communicate (Facebook is used to communicate among the young.) 23. C. to cook (Mary often watches YouTube videos to study how to cook a dish or make a cake.) 24. A. has worked (He has worked for Google since 2014.) Exercise 7: 1. A. We hope having a chance to study together at the same university in the future. (We hope to have a chance to study together at the same university in the future.) 2. B. Lan studied hard for the final test, but she passed with flying colours. (Lan studied hard for the final test, and she passed with flying colours.) 3. C. A group of volunteer students were mowing the lawn in the home for the aged while it started to rain heavily. (A group of volunteer students was mowing the lawn in the home for the aged when it started to rain heavily.) 4. D. She is beautiful and talented, but her parents don't let her to take part in that beauty contest. (She is beautiful and talented, but her parents don't let her take part in that beauty contest.)