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Task 2
Directions: This task is the same as Task 1. The 5 questions or unfinished statements are numbered 41 through 45.
Online services are managed by a host system that maintains a base of information available to satellite users. Users of so-called 'dumb' terminals (i.E.those without processing capability) simply access the information base via programs stored on the system. Personal computer (PC) users typically access the host through a modem(调制解调器). A PC software program serves as an interface (接口) between the server and a PC, allowing the user to operate through the online system and select different databases using a keyboard or a mousE.
National and regional online systems usually have local telephone numbers that PC modems can call to access either a local information base or an indirect long-distance connection, thus reducing long-distance telephone fees. Some online systems allow users to copy large volumes of information onto a local memory storage device, which also reduces the time the user is connected to the online system.
Besides offering a great number of different information bases, ranging from full-text journal libraries to reports of missing children, online services allow users to, for example, reserve airline tickets, buy stocks, purchase goods, and communicate with other users. In exchange for the service, users usually pay a monthly membership feE.They may also pay to connect to various databases on the service or to download information.
Online services work by providing users with ______.
A.a base of information
B.dumb terminals
C.a host system
D.a satellite

A.Online
B.E.those
C.
D.
E.
Online
F.
A.a
G.dumb
H.a
I.a

【参考答案】

A
解析：本题为推理题。根据文章第一段第一句话'Online services are managed by a......

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Eight times within the past million years, something in the Earth's climatic equation has changed, allowing snow in the mountains and the northern latitudes to accumulate from one season to the next instead of melting away. Each time, the enormous ice sheets resulting from this continual buildup lasted tens of thousands of years until the end of each particular glacial cycle brought a warmer climatE.Scientists speculated that these glacial cycles were ultimately driven by astronomical factor: slow, cyclic changes in the eccentricity of the Earth's orbit and in the tilt and orientation of its spin axis. But up until around 30 years ago, the lack of an independent record of ice-age timing made the hypothesis untestablE.Then in the early 1950's Emiliani produced the first complete record of the waxings and wanings of first glaciations. It came from a seemingly odd place, the seafloor. Single-cell marine organisms called 'foraminifera' house themselves in shells made from calcium carbonatE.When the foraminifera die, sink to the bottom, and become part of seafloor sediments, the carbonate of their shells preserves certain characteristics of the seawater they inhabiteD.In particular, the ratio of a heavy isotope of oxygen (oxygen-18) to ordinary oxygen (oxygen-16) in the carbonate preserves the ratio of the two oxygens in water molecules.It is now understood that the ratio of oxygen isotopes reflects the proportion of the world's water locked up in glaciers and ice sheets. A kind of meteorological distillation accounts for the link. Water molecules containing the heavier isotope tend to condense and fall as precipitation slightly sooner than molecules containing the lighter isotopE.Hence, as water vapor evaporated from warm oceans moves away from its source, its oxygen- 18 returns more quickly to the oceans than does its oxygen-16. What falls as snow on distant ice sheets and mountain glaciers is relatively depleted of oxygen-18. As the oxygen-18-poor ice builds up, the oceans become relatively enriched in the isotopE.The larger the ice sheets grow, the higher the proportion of oxygen-18 becomes in seawater--and hence in the sedimentsAnalyzing cores drilled from seafloor sediments, Emiliani found that the isotopic ratio rose and fell in rough accord with the Earth's astronomical cycles. Since that pioneering observation, oxygenisotope measurements have been made on hundreds of cores. The combined record enables scientists to show that the re-cord contains the very periodicities as the orbital processes. Over the past 800, 000 years, the global ice volume peaked every 100,000 years, matching the period of the orbital eccentricity variation. In addition, 'wrinkles' superposed on each cycle--small decreases or surges in ice volume--have come at intervals of roughly 23,000 and 41,000 years, in keeping with the precession and tilt frequencies of the Earth's spin axis.In opening paragraph, the author introduces his topic by ______A.unfolding a phenomenon.B.posing a contrast.C.refuting a speculation.D.testifying a hypothesis.

A.B.
C.
In
D.unfolding
E.
B.posing
F.
C.refuting
G.
D.testifying