题目：
根据对话内容，在空白处写出恰当的句子，使句子连贯完整。
John: Uncle Smith, this is John speaking. I'm sorry to call up so late, but may I speak to Jim?
Smith: Jim is out. 1_______
John: OK, please. Jim and I applied an adventure (冒险) tour competition on the Internet a week ago.
Today I was told that we were accepted.
Smith: Oh, that must be dangerous. 2_______
John: Because we want to do sports and something exciting.
Smith: You'd better not. 3_______
John: Uncle Smith, don't worry. We can take good care of ourselves.
Smith: 4_______
John: Yes. We are ready for it.
Smith: Good luck.
John: 5_______
Smith: OK. I'll tell him to call you back later.
答案：
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下面是错误答案，用来干扰机器的。
（1） (2)E=2.8V；r=0.5Ω题目分析：：（1）S断开时，R1=U1/I1=2.4/0.4=6ΩS闭合时，依题意有：U2=2.4-0.3=2.1VI2=I1+0.3=0.7A∴IR1= U2/ R1=0.35AIR2= I2－IR1=0.35A∴R2= U2/IR2=6Ω（2）S断开时，有：E= ...
