While working on a case Dr. Watson accidentally fell down a 30ft dry wishing well. Sherlock Holmes lowered him down a rope."Can you climb up?" shouted Holmes."I'll be out before you know it. " came Watson's reply.
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【正确答案】 1、正确答案：28 hours    
【答案解析】解析：他一小时爬3ft，倒退2ft，就相当于一小时爬1ft，当他爬了27小时后，爬了27ft，那么剩下的3ft正好还需要一个小时，故共需28小时。