66-70.        The human brain weighs about three pounds and is, without a doubt, the most complex organ in
the human body. This three-pound brain has two halves, left and right, that can easily be seen.
      People used to think that certain activities such as logical thinking and speech occurred only in
the left half of the brain and other things like writing, music, art, and so on, occurred only in the
right half of the brain.
      In recent years, new technology has made it possible to study the brain in great detail. We can
see which parts of the brain are being used during a human activity such as watching a ball game,
reading a book, solving a math problem, and so on. Now we know that many parts of the brain work
together at the same time when a human is listening to music, reading a story, or learning math.
      When the brain has been injured, other parts of the brain try to take over the work the injured
part was doing. Now we understand that the brain is very flexible and it never stops learning.
Scientists are learning how to grow new cells to repair parts of the brain that have been injured.
【題組】67. What is the main concern of this passage?
(A) Recent medical research on humans.
(B) Discoveries of left and right halves of the brain.
(C) How the human brain functions.
(D) The secrets of human brains.