[单项选择]

Although a given waveform may contain frequencies over a very broad range, as a practical matter any transmission system will be able to accommodate only a limited band of （1）. This, in turn, limits the data rate that can be carried on the transmission （2）. A square wave has an infinite number of frequency components and hence an infinite （3）. However, the peak amplitude of the kth frequency component, kf, is only l/k, so most of the （4） in this waveform is in the first few frequency components. In general, any digital waveform will have（5） bandwidth. If we attempt to transmit this waveform as a signal over any medium, the transmission system will limit the bandwidth that can be transmitted.

（2）是（）
A. procedures
B. function
C. route
D. medium

[单项选择]

Although a given waveform may contain frequencies over a very broad range, as a practical matter any transmission system will be able to accommodate only a limited band of （1）. This, in turn, limits the data rate that can be carried on the transmission （2）. A square wave has an infinite number of frequency components and hence an infinite （3）. However, the peak amplitude of the kth frequency component, kf, is only l/k, so most of the （4） in this waveform is in the first few frequency components. In general, any digital waveform will have（5） bandwidth. If we attempt to transmit this waveform as a signal over any medium, the transmission system will limit the bandwidth that can be transmitted.

（1）是（）
A. frequencies
B. connections
C. diagrams
D. resources

[单项选择]Although numbers of animals in a given region may fluctuate from year to year, the fluctuations are often temporary and, over long periods, trivial. Scientists have advanced three theories of population control to account for this relative constancy.
The first theory attributes a relatively constant population to periodic climatic catastrophes that decimate populations with such frequency as to prevent them from exceeding some particular limit. In the case of small organisms with short life cycles, climatic changes need not be catastrophic: normal seasonal changes in photoperiod (daily amount of sunlight), for example, can govern population growth. This theory—the density independent view—asserts that climatic factors exert the same regulatory effect on population regardless of the number of individuals in a region.
A second theory argues that population growth is primarily density-dependent—that is, the rate of growth of a population in a region decreases as the number of an
A. Famine.
B. Tornadoes.
C. The number of predators.
D. The variety of food supply.

[单项选择]

A simple pair of pants may contain a multitude of meanings. In the 1850s, jeans were the unemotional, durable dress of those that came to California to labor in the gold fields. Seams were strengthened with metal pins to make them hold, a technology borrowed from the construction of horse blankets. Cloth for beasts of burden was translated to the needs of men of burden. These were the clothes of hard-laboring people, and these pants held little promise for the men who wore them, save the promise that they would be ready for the next day’s labors.
During the same decade, in the court of one European queen, "the gown worn by a fashionable lady in attendance contained 1,100 yards of material not including lace and other ornaments." American women of wealth were also wrapped in an abundance of cloth. While makers of jeans worried over how many men could be fitted into a given amount of cloth, for women of wealth the concern was with how many yards of cloth cou
A. rescue
B. preserve
C. put aside
D. except