When is the density of the water required to be logged in the logbook of a ship？A.Any time

ship？

A.Once a day

B.Once a week

C.Prior to getting underway

D.Only when entering waters of different density

the exact ranges of other ships or objects in the vicinity．

A.Radar

B.GPS

C.DF

D.Satellite Navigator

A.形状 Shape

B.重量 Weight

C.体积 Volume

D.频率 Frequency

E.密度 Density

A.形状 Shape

B.重量 Weight

C.体积 Volume

D.频率 Frequency

E.密度 Density

when

A.smoke density has been decreased sufficiently to see the bulkhead opposite the compartment's entrance

B.a lifeline and explosion proof flash light are used

C.all smoke and toxic fumes are removed and an adequate oxygen supply is present

D.overhaul has been completed to remove any possible source of re-ignition

A.含量居第二。无色气体Colorless gas.###SXB###B.比空气稍重，lNm3乙烷重1.271kg。Slightly heavier than air, lNm3 ethane weighs 1.271kg.###SXB###C.它的热值在60345～65946kJ/m3。Its calorific value is 60345 ~ 65946kJ/m3.###SXB###D.在20℃条件下，加压至3.8MPa以上时，可液化成为相对密度0.446的液体。Under the condition of 20℃, the liquid can be liquefied to a relative density of 0.446 when pressurized to more than 3.8MPa.###SXB###E.天然气中的含量一般在0.05~25%之间。Natural gas typically contains between 0.05 and 25 percen

A.含量居第二。无色气体Colorless gas.###SXB###B.比空气稍重，lNm3乙烷重1.271kg。Slightly heavier than air, lNm3 ethane weighs 1.271kg.###SXB###C.它的热值在60345～65946kJ/m3。Its calorific value is 60345 ~ 65946kJ/m3.###SXB###D.在20℃条件下，加压至3.8MPa以上时，可液化成为相对密度0.446的液体。Under the condition of 20℃, the liquid can be liquefied to a relative density of 0.446 when pressurized to more than 3.8MPa.###SXB###E.天然气中的含量一般在0.05~25%之间。Natural gas typically contains between 0.05 and 25 percen

A.放在该点的通电直导线所受的磁场力的方向The direction of the magnetic force on the current-carrying placed at this point

B.放在该点的正检验电荷所受的磁场力的方向The direction of the magnetic force on the positive charge placed at this point

C.放在该点的小磁针静止时N极所指的方向The direction of N pole when the small magnetic needle placed at this point is stationary

D.通过该点磁场线的切线方向Tangent direction of magnetic field line at this point

of social demands. However, Mexico will still be far from the "aging societies" that will most likely prevail (占优势 ) in the industrialized countries. In less than 25 years, the country will have to add almost as much infrastructure as it has already built up to now, simply to maintain services and production at the current levels. This will be a tremendous challenge, although a similar one was faced successfully in the recent past, when available infrastructure was doubled in two decades or so. It is no wonder that much has been said about the need to reduce or preferably halt Mexico's population control which is taken for granted as both good and necessary. It has also gained supporters in the developing world, and Mexico is no exception. But the arguments about population are complicated, as the following discussion illustrates. Even if Mexico's population reaches 125 million by the year 2010, its population density is still smaller than the 1985 population density of some 50 countries. By international standards Mexico will still not be overpopulated by the year 2010. If wealth is generated by people, the more individuals there are, the greater the wealth that potentially could be generated. Why should Mexico control its population at density levels below those of the richer countries if more population represents the possibility of generating more wealth？ On the other hand, it is often pointed out that once sustainability(支撑力) limits are near or are reached, there are decreasing productivity gains (or,perhaps more accurately, increasing productive losses) , and people become a cost rather than an asset. If we assume that there are sustainability limits and that we are close to reaching these limits at a world level, then it is appropriate to check population growth. According to the passage, the population argument is focused on_______.

A.whether more people are a property or a cost

B.whether Mexico should control its population growth or not

C.whether the density of population in Mexico is large or small

D.what the standard international sustainability limit is

What is a black hole？ Well, it is difficult to answer the question,

as the terms we would normally use to describe a scientific phenomenon __1__are adequate here. Astronomers and scientists think that a black hole is __2__a region of space which matter has fallen and from which nothing can __3__

escape—not even light. But we can’t see a black hole. A black hole __4__exerts a strong gravitational pull and yet it has no matter. It is only space—or thus we think. How can this happen？ __5__

The theory is that some stars explode when their density increases to a particular point; they “collapse” and sometimes a supernova occurs.

The collapse of a star may produce a “White Dwarf” of a “neutronstar”—

a star which matter is so dense that if continually shrinks by the force of __6___its own gravity. But if the star is very large, this process of shrinking may be so intense that a black hole results in. Imagine the earth reduced to the __7__size of a marble, but still having the same masses and a stronger __8__gravitational pull, and you have some ideas of the force of a black hole. __9__And no matter near the black hole is sucked in. __10__