梧桐与法国梧桐是不是同一种树？

城市绿地系统是指( )。

A．以自然和人工植被为地表主要存在形态的城市用地，包括城市建设用地范围内用于绿化的土地和城市建设用地之外对城市生态、景观和居民休闲生活具有积极作用、绿化环境较好的特定区域

B．对各种城市绿地进行定性、定位、定量的统筹安排，形成具有合理结构的绿色空间系统，以实现绿地所具有的生态保护、游憩休闲和社会文化等功能

C．保持城市生态系统的平衡，满足城市居民的户外游憩需求，满足卫生和安全防护、防灾、城市景观的要求

D．城市中具有一定数量和质量的各类绿化及其用地，相互联系并具有生态效益、社会效益和经济效益的有机整体

下列属于统计行政法规的是（）。

A．《统计法实施细则》

B．《全国经济普查条例》

C．国家统计局制定的《统计执法检查规定》

D．国家统计局制定的《统计从业资格认定办法》

E．《全国农业普查条例》

如图为重2N的木块，用力的示意图画出木块受到的重力．

Did you ever wonder why leaves change colors in autumn, or how it happens? Here’s a quick explanation.

First of all, you’ve probably noticed that not all trees lose their leaves. There are two major types of trees: deciduous trees and evergreens. Evergreens keep their leaves and stay green all year long. The deciduous trees are the ones that lose their leaves each year.

In autumn, the days begin to get shorter. The sun is also lower in the sky at noon, which causes temperatures to be cooler. The combination of less sunshine and lower temperatures is what causes the deciduous trees to drop their leaves. In winter, deciduous trees “go to sleep”, sort of like a bear goes into hibernation.

Leaves are the food factories for a plant. Unlike animals，plants make their own food by taking energy directly from the sun. Plants do this by using a chemical in their leaves called chlorophyll.

Chlorophyll is green. During the spring and summer the leaves of a deciduous tree look green because there is a lot of chlorophyll there. In autumn, however, the sunshine becomes more  scarce and the leaves on the trees stop making new chlorophyll. As the old chlorophyll starts to break down, the green color of the leaf begins to go away.

You’ve probably also noticed that the leaves of different kinds of trees change different colors. The leaves of some trees turn yellow or orange, while the leaves of other trees turn bright red or purple. The different colors are caused by the different chemical reactions that are happening in the leaves.

For example, the leaves of some trees turn yellow when the chlorophyll breaks down. When the green chlorophyll goes away, a yellow pigment in the leaf becomes visible. The yellow pigment, called cartenoid, was already there during the summer, but is was not easily seen because there was too much green chlorophyll.

In other trees where the leaves turn red or purple a different chemical reaction takes place. In those leaves the chlorophyll also breaks down, but another chemical reaction takes place at the same time. Chemicals in the leaves, called starches, begin to change into chemicals called anthocyanins, which give the leaves their red and purple colors.

So next time you see the beautiful colors of autumn you will also know the science behind that beauty.

46.   What is the correct term for trees that lose their leaves in the autumn?

A. Evergreens       B. Deciduous        C. Cartenoids  D. Anthocyanins

47.   Which of the following is NOT mentioned as a cause of trees dropping their leaves?

A. A change in temperature   B. The amount of daylight available

C. Extra chlorophyll         D. Chemical changes in the leaves

48.   If there are 50 evergreens and 10 deciduous trees in a forest, in autumn what color are most of the leaves in the forest likely to be?

A. Green B. Red and purple

C. Yellow        D. not enough information to determine the answer

49.   Which of the following is only present in leaves during the autumn?

A. Chlorophyll       B. Starch C. Cartenoids        D. Anthocyanins

50.   Where would such an article mostly likely be published?

A. In a book                   B. In a primary school science text book

C. In a magazine for young people       D. All are equally likely

选用专项工种罪犯必须坚持的原则（）

A、严格条件

B、严格管理

C、考核

D、任人为贤