单选题
In their world of darkness, it would seem likely
that some of the animals might have become blind, as has happened to some cave
fauna. So, indeed, many of them have, compensating for the lack of eyes with
marvelously developed feelers and long, slender fins and processes with which
they grope their way, like so many blind men with canes, their whole knowledge
of friends, enemies, or food coming to them through the sense of
touch. The last traces of plant life are left behind in the
thin upper layer of water for no plant can live below about 600 feet even in
very clear water, and few find enough sunlight for their food-manufacturing
activities below 200 feet. Since no animal can make its own food, the creatures
of the deeper waters live a strange, almost parasitic existence of utter
dependence on the upper layers. These hungry carnivores prey fiercely and
relentlessly upon each other, yet the whole community is ultimately dependent
upon the slow rain of descending food particles from above. The components of
this never-ending rain are the dead and dying plants and animals from the
surface, or from one of the intermediate layers. For each of the horizontal
zones or communities of the sea that lie between the surface and the sea bottom,
the food supply is different and in general poorer than for the layer
above. Pressure, darkness, and silence are the conditions of
life in the deep sea. But we know now that the conception of the sea as a silent
place is wholly false. Wide experience with hydrophones and other listening
devices for the detection of submarines has proved that, around the shore lines
of much of the world, there is the extraordinary uproar produced by fishes,
shrimps, porpoises and probably other forms not yet identified. There has been
little investigation as yet of sound in the deep, offshore areas, but when the
crew of the Atlantis lowered a hydrophone into deep water off Bermuda, they
recorded strange mewing sounds, shrieks, and ghostly moans, the sources of which
have not been traced. But fish of shallower zones have been captured and
confined in aquaria, where their voices have been recorded for comparison with
sounds heard at sea, and in many cases satisfactory identification can be
made. During the Second World War the hydrophone network set up
by the United States Navy to protect the entrance to Chesapeake Bay was
temporarily made useless when, in the spring of 1942, the speakers at the
surface began to give forth, every evening, a sound described as being like "a
pneumatic drill tearing up pavement". The extraneous noises that came over the
hydrophones completely masked the sounds of the passage of ships. Eventually it
was discovered that the sounds were the voices of fish known as croakers, Which
in the spring move into Chesapeake Bay from the offshore wintering grounds. As
soon as the noise had been identified and analyzed, it was possible to screen it
out with an electric filter, so that once more only the sounds of ships came
thorugh the speakers.
单选题
Many underwater animals cannot see because ______.
A. the lack of light has gradually eliminated their capacity to see
B. they use sound waves instead of light to navigate in the darkness
C. they have learned to survive without seeing their enemies or their
prey
D. their sense of touch has eliminated their need to see