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11.Keeping the environment clean is very important
=>It...
12."I will have an English test tomorrow"
=>He said that...
14.Althought they were tired ,they tried to finish their project on time.
=>In spite of...
15."We may go sightseeing in Sapa next week "
=>My friends told me that...
18.I last visited London was two year ago
=>I haven't...