21. According to the passage, scientists are able to use ocean acoustic tomography to deduce the properties of the oceans interior in part because
low-frequency sound waves are well described mathematically
mesoscale phenomena are so large as to be easily detectable
information from sound waves can be recombined more easily than information from x-rays
tomography is better suited to measuring mesoscale phenomena than to measuring small-scale systems
density variations in the ocean are mathematically predictable
22. The passage suggests that medical tomography operates on the principle that
x-rays are superior to sound waves for producing three-dimensional images
sound waves are altered as they pass through regions of varying density
images of the bodys interior can be produced by analyzing a single x-ray transmission through the body
the varying densities within the human body allow x-rays to map the internal organs
information from x-rays and sound waves can be combined to produce a highly detailed image of the bodys interior
23. Which of the following is most similar to medical tomography as it is described in the passage?
The use of ocean-current meters to determine the direction and velocity of the oceans mesoscale fields
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