调查人员根据自己的经验判断出有代表性的个体作为样本，该种抽样调查是（）。A.便利抽样

阅读理解。

     Do you know that you can use your watch as a compass (指南针) on a sunny day? Take a watch and point

the hour hand in the direction of the sun. Imagine a line which runs from the center of the watch through a point

half way between the hour hand and number one. This line will surely point south.

     If you know astronomy a little, you will understand why this works. In the northern half of the earth, the sun

is in the south at noon. In Russia, the real noon is one o'clock. If at that time we point the hour hand at the sun,

the hour hand and the number one will point south. That is why you must imagine a line which will run from the

center of the watch through a point half way between the hour hand and number one. It will point south. If you

are in the southern part of our planet, you must point number 12 at the sun. The line which you can imagine

between number twelve and the hour hand will then show north.

1. When we carry out this experiment in the northern part of the earth, we should point _____ at the sun.

A. number 12

B. the minute-hand

C. the hour hand

D. number one

2. What does the word "astronomy" mean in this passage?

A. 天文学

B. 地理学

C. 宇航学

D. 逻辑学

3. The passage tells us that we can use a watch _____ on a sunny, day.

A. to study the weather

B. to show direction

C. to enjoy ourselves

D. to keep good time

4. If you are in Australia, which tithe following is the,right way to show north?

                  A                              B                            C                            D

5. What's the best title for this passage?

A. Your Watch Becomes a Compass

B. The Story of a Watch

C. An Interesting Watch

D. The Sun and a Watch

关于X线检查不正确的是：（）。

A.首次X线检查即可确定有无骨折

B.X线检查须与临床相结合

C.某些部位需要特殊体位投照

D.四肢X线检查需要包括一个关节

E.骨骺损伤X线检查不能确定

液体的黏滞系数随着温度的升高而升高。

预塔回流比是（），加压塔回流比是（），常压塔回流比（）。