潜伏期计算，一般应遵循下列哪些基本原则？（）A.选择单次暴露病例B B.纳入疑似、临

根据对话内容，从方框内的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
A: Jim ,how will you spend your summer holidays this year?
B: I’ll go back to London and enjoy watching TV.
A:   1  .
B: Sports. I’m glad that the 30^th Olympic Games will be held in our country soon.
A: I know you are a sports fan.____2___ .
B: They’re held every four years.
A: __3_____.
B:Yes.
A: Thanks . But I’ve one more question.   4  .
B: Don’t you know it will be held in London this August？
A: ___5____ .I hope that day will come soon. .

By the way, how often are the Olympic Games held? That’s wonderful. Why not go to Beijing with your friend? What kind of TV program do you like？ When will England hold the 30th Olympic Games？ How do you like sports? Just like the Football World Cup?