[填空题]

Vision

Human vision like that of other primates(灵长类) has evolved in an arboreal(丛林) environment. (46)
In the course of evolution, members of the primate line have acquired large eyes while the nose has shrunk. (47) Of mammals(哺乳动物) only humans and some primates enjoy color vision. (48) Horses live in a single-color world.
Light visible to human eyes, however, occupies only a very narrow band in the whole electromagnetic spectrum(光谱). Ultraviolet rays(紫外线) are invisible to humans though ants and honeybees are sensitive to them. (49) The world would look terribly different if human eyes were sensitive to infrared radiation(红外线). Then instead of the darkness of night, we would be able to move easily in a strange shadowless world. (50)
The color sensitivity of normal human vision is rarely surpassed even by complicated technical devices.

• A. Humans have no direct perception of
  

[填空题]
Human vision like that of other primates(灵长类) has evolved in an arboreal(丛林) environment. (46)
In the course of evolution, members of the primate line have acquired large eyes while the nose has shrunk. (47) Of mammals(哺乳动物) only humans and some primates enjoy color vision. (48) Horses live in a single-color world.
Light visible to human eyes, however, occupies only a very narrow band in the whole electromagnetic spectrum(光谱). Ultraviolet rays(紫外线) are invisible to humans though ants and honeybees are sensitive to them. (49) The world would look terribly different if human eyes were sensitive to infrared radiation(红外线). Then instead of the darkness of night, we would be able to move easily in a strange shadowless world. (50)
The color sensitivity of normal human vision is rarely surpassed even by complicated technical devices.

• A. Humans have no direct perception of
  

[填空题]Human vision like that of other primates has evolved in an arboreal
environment. In the dense complex world of a tropical forest, it is more
important to see well to develop an acute sense of smell, in the 41 ______
course of evolution members of the primate line has acquired large 42 ______
eyes while the snout has shrunk to give the eye an unimpeding view. 43 ______
Of mammals only humans and some primates enjoy color vision. The red
flag is black to the bull. Horses live in a monochrome world. Light visible to
human eyes, therefore, occupies only a very narrow band in the whole 44 ______
electromagnetic spectrum. Ultraviolet rays are invisible to humans though
ants and honeybees are insensitive to them. Humans have no direct perception 45 ______
of infrared rays like the rattlesnake that has receptors tuned into 46 ______
wavelengths long