质量相同的尘粒因形状不同，在沉降时所受阻力也不同，因此，粉尘的形状能影响其( )。

黑光灯是利用物理方法灭蛾杀虫的-种环保型设备，它发出的紫色光能够引诱害虫飞近黑光灯，然后被黑光灯周围的交流高压电网“击毙”．

（1）-只额定功率为P的黑光灯正常工作时，约有5%的电能转化为光能，光能中约有50%是频率为υ的紫光．求黑光灯每秒钟向外辐射多少个该频率的紫光光子．（已知普朗克恒量为h）

（2）如图是高压电网的工作电路示意图，变压器将有效值为220V的交流电压变成高压，输送到高压电网，电网相邻两电极间距离为0.5cm．空气在常温常压下被击穿的临界电场强度为6220V/cm，为防止两电极间空气被击穿而造成短路，变压器的初、次级线圈匝数比n₁：n₂应满足什么条件？．

以下哪项不是我国常见的会计期间？（ ）

A．1月1日起至12月31日

B．1月1日起至6月30日

C．6月1日起至9月30日

D．2月1日起至2月28日

侧置气门式气缸（）附近磨损较大。

A.进气门

B.进气门对面

C.排气门对面

D.排气门

In our society, we must communicate with other people. A great deal of communicating is performed on a person-to-person (1) by the simple means of speech. If we travel in buses, stand in football match (2) , we are likely to have conversations (3) we give information or opinions, and sometimes have our views (4) by other members of society.

Face-to-face contact is (5) the only form of communication, and during the last two hundred years the (6) of mass communication has become one of the dominating factors of contemporary society. Two things, (7) others, have caused the enormous growth of the communication industry. Firstly, inventiveness has (8) advances in printing, photography and so on. Secondly, speed has revolutionized the (9) and reception of communications so that local news often (10) a back seat to national news.

No longer is the possession of information (11) to a privileged minority. Forty years ago people used to (12) to the cinema, but now far more people sit at home and turn on the TV to watch a program that (13) into millions of houses. Communication is no longer merely concerned (14) the transmission of information. The modern communications industry influences the way people live in society and broadens their horizons by allowing (15) to information, education and entertainment. The printing, broadcasting and advertising industries are all (16) with informing, educating and entertaining. (17) a great deal of the material communicated by the mass media is very valuable to the individual and to the society (18) which he is a part, the vast modern network of communications is (19) to abuse. However, the mass media are with us for better, for worse, and there is no turning (20) .

16（）

A.engaged

B.involved

C.occupied

D.dealt

何谓水的碱度。