在海产品中，大量存在的致病菌是（） A.沙门菌 B.金黄色葡萄球菌 C.变形弧菌 D

一组数据均同加（或同减）一个常数（不为0的数）后（）。

A.均数不变

B.标准差不变

C.中位数不变

D.变异系数不变

E.以上都变

用divide和separate或其构成的短语的正确形式填空

1. Fifteen _       by 3 is 5.

2. Will you___      _the bad apples _    the good ones?

3. Let's       ourselves____ several groups.

4. We          the money equally.

5. English is____   ____ France by the English Channel.

以下哪种情况与生长发育规律不符（）

A.生长发育有个体差异

B.生长发育是连续的过程

C.各系统、器官发育不平衡

D.神经系统发育先慢后快

E.生长发育遵循从上到下，从近到远，由粗到细，由简单到复杂的规律

[说明]

某宾馆拟开发一个宾馆客房预订子系统，主要是针对客房的预订和入住等情况进行管理。

[需求分析]

(1) 员工信息主要包括：员工号、姓名、出生年月、性别、部门、岗位、住址、联系电话和密码等信息。岗位有管理和服务两种。岗位为“管理”的员工可以更改(添加、删除和修改)员工表中本部门员工的岗位和密码，要求将每一次更改前的信息保留；岗位为“服务”的员工只能修改员工表中本人的密码，且负责多个客房的清理等工作。
(2) 部门信息主要包括：部门号、部门名称、部门负责人和电话等信息。一个员工只能属于一个部门，一个部门只有一位负责人。
(3) 客房信息包括：客房号、类型、价格和状态等信息。其中类型是指单人间、三人间、普通标准间和豪华标准间等，状态是指空闲、入住和维修。
(4) 客户信息包括：身份证号、姓名、性别、单位和联系电话。
(5) 客房预定情况包括：客房号、预定日期、预定入住日期、预定入住天数和身份证号等信息。一条预定信息必须且仅对应一位客户，但一位客户可以有多条预定信息。

[概念模型设计]

根据需求阶段收集的信息，设计的实体联系图(不完整)如图8-3所示。

[逻辑结构设计]

逻辑结构设计阶段设计的部分关系模式(不完整)如下。
员工( (4) ，姓名，出生年月，性别，岗位，住址，联系电话，密码)
权限(岗位，操作权限)
部门(部门号，部门名称，部门负责人，电话)
客厉( (5) ，类型，价格，状态，入住日期，入住时间，员工号)
客户( (6) ，姓名，性别，单位，联系电话)
更改权限(员工号， (7) ，密码，更改日期，更改时间，管理员号)
预定情况( (8) ，预定日期，预定入住日期，预定入住天数)
1. 根据问题描述，填写图8-3中的(1)～(3)空缺处联系的类型。联系类型分为一对一、一对多和多对多3种，分别使用1:1，1:n或1:*，m:n或*:*表示。

The city water pipes in Rome were usually of baked clay or lead; copper was sometimes used and also hollowed stone. For the large supply conduits leading to the city the Romans used covered channels with free water surfaces, rather than pipes. Perhaps this choice was a matter of economics, for apparently they could make lead pipes up to 15 inches in diameter. While pipes can follow the profile of undulating ground, with the pressure increasing in the lower areas, channels cannot. They must slope continuously downwards, because water in channels does not normally flow uphill; and the grade must be flat, from 1 in 60 in small channels to perhaps 1 in 3,000 in large ones, to keep the water speed down to a few feet per second. Thus the main supply channels or aqueducts had long lengths of flat grade and where they crossed depressions or valleys they were carried on elevated stone bridges in the form of tiered arches. At the beginning of the Christian era there were over 30 miles of these raised aqueducts in the 250 miles of channels and tunnels bringing water to Rome. The channels were up to 6 feet wide and 5 to 8 feet high. Sometimes channels were later added on the tops of existing ones. The remains of some of these aqueducts still grace the skyline on the outskirts of Rome and elsewhere in Europe similar ruins are found.

Brick and stone drains were constructed in various parts of Rome. The oldest existing one is the Cloaca Maxima which follows the course of an old stream. It dates back at least to the third century B.C. Later the drains were used for sewage, flushed by water from the public baths and fountains, as well as street storm run-off.

The truly surprising aspect of the achievements of all the ancient hydraulic artisans is the lack of theoretical knowledge behind their designs. Apart from the hydrostatics of Archimedes, there was no sound understanding of the most elementary principles of fluid behaviour. Sextus Frontinus, Rome’s water commissioner around A.D. 100, did not fully realize that in order to calculate the volume rate of flow in a channel it is necessary to allow for the speed of the flow as well as the area of cross-section. The Romans’ flow standard was the rate at which water would flow through a bronze pipe roughly 4/3 inch in diameter and 9 inches long. When this pipe was connected to the side of a water-supply pipe or channel as a delivery outlet, it was assumed that the outflow was at the standard rate. In fact, the amount of water delivered depended not only on the cross-sectional area of the outlet pipe but also on the speed of water flowing through it and this speed depended on the pressure in the supply pipe.

In order to calculate the volume of water flowing through a pipe, it is important to know its speed and（）

A．the area across the end of the pipe

B．the length of the pipe

C．the water pressure in the pipe

D．the level from which the water falls