单项选择题

Lack of technological progress in the ancient and medieval worlds was primarily due to the absence of ______.

A．natural resources
B．inventive ability
C．people's desire for the "better things of life"
D．proper social organization
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单项选择题
Whether a colored object would, on two viewings separated in time, appear to the viewer as similar or different in color would depend mostly on ______.
A．the color mechanism of the eye in use at the time of each viewing
B．whether the object was seen in artificial or natural light
C．what kind of viewing had immediately preceded each of the viewings
D．the individual's power of lateral adaptation
单项选择题
This selection is primarily concerned with ______.
A．the eye's adaptation to color
B．the properties of colored surfaces
C．the color of colors
D．the effect of changes in color intensity
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