简述植物流行性病害的概念及病害流行必需的条件。

Happy Life Swimming Club Rules
1. All swimmers must take a bath before they go into the pool (游泳池).
2. Diving (跳水) is only allowed unless you have been a member for at least 1 year.
3. Running and playing near the pool are not allowed.
4. Club members can bring guests only at weekends.
5. Children under 12 are not allowed to use the pool unless their parents are with them.
6. Members must show their membership cards before going inside.
7. Smoking is not allowed in the room for changing clothes.
8. Guests must write down their names before going inside.
9. All members must leave before 6 P.M. at workdays.
10. All members must leave before 10 P.M. at weekends.
11. Clothes must be put in the lockers (带锁柜厨).
12. Keep your key of the lockers along with you. If it is lost, you must report to the manager as soon as possible.
13. Only club members and their families are allowed to use the pool.

If you have been in this club for half a year, can you dive
[A] Yes.
[B] No.
[C] Doesn’t say.

在城市规划保留现有城市中的历史文化价值的古城墙、古建筑、文化古迹、历史街区的重要意义是( )。

A．作为历史遗产而保留

B．作为城市历史的见证而保留

C．为了保护和延续古城风貌特点，继承和发扬传统文化需要

D．作为发展旅游业的一种资源而保留

下面关于债券的叙述正确的是( )。

A．债券尽管有面值，代表了一定的财产价值，但它也只是一种虚拟资本，而非真实资本

B．债权人除了按期取得本息外，对债务人也可以作其他干预

C．由于债券期限越长，流动性越差，风险也就越大，所以长期债券的票面利率肯定高于短期债券的票面利率

D．流通性是债券的特征之一，也是国债的基本特点，所有的国债都是可流通的

在升级BIOS时，下列哪项是重点要考虑的（）。

A.写入新的BIOS程序

B.获得最新版本的BIOS程序

C.获得相同版本的BIOS程序

D.清除现有的BIOS程序

比体积和密度是成正比例关系。