A、Artificial hearts. B、Telescopes. C、Microscopes. D、Radio telescopes. C文中可以听到：Early in the 17th century a new instrument came in

As is known to all, scientists and philosophers had studied the human body and its functions from very early times. Unfortunately, many of the ideas and theories, correct and incorrect, were accepted without question for a great number of years. But by the 16th century, knowledge gained through chemical experiments was beginning to make some people think more deeply about how the human body works.
    A most important medical discovery was made by William Harvey in 1628. He found out that the blood is circulated round the body in one direction only by the pumping action of the heart. It had previously been incorrectly thought that the blood moved with a backward and forward motion.
    Early in the 17th century a new instrument came into use that was to open up a whole new area in the study of medical and scientific matters. This was the microscope.
    The first instruments were not very efficient. They were able to magnify only a very small part of the object and this was always surrounded by rings of coloured light. Nevertheless a great step forward had been taken which was of vital importance for future research and development.