A、Part of a medical textbook. B、A medical journal. C、Some microscope slides. D、The speaker’s current research. A根据文章开头的“the main

To quickly review the main points covered in Chapter seven, the most important part of the system of nerves is the brain. The brain controls most of the body’s activities. Messages between the brain and the spinal cord are carried by nerves which are made up of special cells called nerve cells. Nerve cells are found in the brain, spinal cord, spinal nerves and the organs we use to see, hear, smell, taste and touch.
    Nerve cells have long, string-like fibers that carry messages. These fibers have branched ends to send and receive messages. Remember that nerve cells are so small that they can’t be seen without a microscope. But one fiber from a nerve cell may stretch as long as three feet.
    There are many kinds of nerve cells and this chapter deals mainly with three kinds. The sensory nerve cells carry messages of heat, light, sound and pressure from the skin, muscles and organs inside the body. Motor nerve cells carry messages to the muscles and this causes the muscles to move. Connecting nerve cells go between the sensory nerve cells and motor nerve cells. After the messages go from the spinal cord to the brain, the brain sends messages through the motor nerve cell to the muscles. All these different nerve cells help us see, hear, taste, smell and feel. Now, if you have no further questions about Chapter 7, we’ll go on to talk about the chemical processes involved in this transfer of messages.
Questions 26-30 are based on the passage you have just heard:
26. What is the source of the speaker’s information?
27. What role do nerve fibers play?
28. What does a nerve fiber look like according to the speaker?
29. How many kinds of nerve cells are discussed in this talk?
30. Which of the following nerve cells sends messages to the muscles?