问题 问答题

(1)在①试管、②烧杯、③烧瓶、④量筒、⑤天平、⑥酒精灯、⑦铁架台七种仪器中:

①不能加热也不能用作反应容器的是______;

②在常温或加热时,进行少量试剂反应的容器是______;

③用如图所示装置制取蒸馏水时,用到的仪器有______.

(2)在探究燃烧的条件时,老师应用“控制变量”的方法做了如图所示的实验,可观察到放在薄铜片上的白磷燃烧、红磷不燃烧.由此实验可知:

燃烧需要有可燃物、氧气(或空气)和______;依据燃烧条件,老师控制白磷和红磷的变化因素

是______,控制白磷和红磷的不变因素有______(要求写出三点).

(3)由上述实验可知,若遇到电器意外失火应采取的措施是______(填序号).

A.用泡沫灭火器B.立即切断电源C.用沙土掩埋D.用湿棉被盖灭.

答案

(1)对常用化学仪器的了解和识记,得知:①不能加热也不能用作反应容器的是量筒;②在常温或加热时,进行少量试剂反应的容器是:试管;③制取蒸馏水时,用到的仪器有:试管、烧杯、烧瓶、酒精灯、铁架台.

(2)在探究燃烧的条件时,应用“控制变量”的方法做了实验,从而验证可燃物的燃烧条件;拓展灭火原理.

故答案为:(1)①量筒(或④)   ②试管(或①)    ③试管、烧杯、烧瓶、酒精灯、铁架台(或①、②、③、⑥、⑦)

(2)①一定的温度(或达到着火点)     ②它们的着火点不同        都是可燃物质、都露置在空气中、都在相同温度下

(3)B、D(或B、A)

单项选择题
单项选择题

Workforce is defined as the total number of people who are available to work and earn incomes. The definition includes everyone who is employed or seeking paid employment, so it includes employers and the self-employed.

Although the size of the workforce depends a great deal on the size of the total population, there are several other influences which also affect it. The age distribution of the total population has a very marked effect on the available workforce. If the population has a high proportion of very young people or of those too old to work, then the available workforce would be lower than if there were an evenly spread age distribution. If the population grows rapidly from natural increase, i.e., the number of births greatly exceeds the number of deaths, then as the total population increases, the proportion in the workforce declines

Sometimes a population is described as aging, which means that the birth rate is either falling or growing very slowly, and as people retire from the workforce, there are not enough young people entering it to replace those who are leaving it. The population is top-heavy with older people. So the percentage of the population in the workforce declines when there is either a rapid increase in births or a falling birth rate.

The age distribution of the population has several important effects on the economy. If the population is aging and there is an increase in the number of people retiring without a corresponding increase in the number entering the workforce, this raises the problem of the ability of the economy to provide a reasonable level of social services to the retired group. If the aged are to be cared for in special homes or hotels, finances must be available for that purpose. If the size of the workforce is small relative to the total population, then the government tax receipts are relatively low and either the government has less money available to it or the workforce members have to be taxed more heavily.

Workforce is composed of ().

A. both the employed and the self-employed

B. people employed to work for others

C. both employers and employees

D. people available to work and earn incomes