[单项选择]Although they plant trees in this area every year the tops of some hills are still ________.


A. blank
B. hollow
C. vacant
D. bare

[单项选择]Although they plant trees in this area every year, the tops of some hills are still______.
A. blank
B. hollow
C. vacant
D. bare

[单项选择]Though people plant many trees in this area every year, the top of some hills is still ______.
A. open
B. empty
C. bare
D. blank

[单项选择]We were delighted to find the trees planted a year before ______ very tall.
A. growing
B. being grown
C. having been growing
D. grown

[单项选择]Statistics indicate that approximate every 22 years--within a range of 3 to 4 years--a major drought occursin the United States.

[单项选择]What happens to trees each year


A. Their tings get thinner and thinner.
B. They add a ring of wood.
C. Their rings get darker in color.
D. They become more valuable.

[单项选择]

Every year television stations receive hundreds of complaints about the loudness of advertisements. However, federal rules forbid the practice of making ads louder than the programming. In addition, television stations always operate at the highest sound level allowed for reasons of efficiency. According to one NBC executive, no difference exists in the peak sound level of ads and programming. Given this information, why do commercials sound so loud
The sensation of sound involves a variety of factors in addition to its peak level. Advertisers are skilful at creating the impression of loudness through their expert use of such factors. One major contributor to the perceived loudness of commercials is that much less variation in sound level occurs during a commercial. In regular programming the intensity of sound varies over a large range. However, sound levels in commercials tend to stay at or near peak levels.
Other "tricks of the trade" are also used. B
A. the human voices in commercials have more auditory impact
B. people like cheerful songs that change dramatically in sound quality
C. high-frequency sounds are used to mask sounds that drown out the primary message
D. they possess sound qualities that make the viewer feel that something unusual is happening