3Dear LiMing，This week in school， we discussed transportation.We learned about trains， planes， bicycles， cars and rockets.亲爱的李明，这个星期在学校里，我们讨论了交通工具。
15SOS is a code that was used in an old form of communication called Morse Code. It is a call or signal for help.15.1code名词，密码;
【课文原文】His teacher wrote a big “F” for “fail” on his English exam paper.23 tell sb. sth. = tell sth. to sb. 告诉某人某事。24 because of 因为。
