The correct answer is D. Show how stringed instruments have several different characteristics.
Step-by-step explanation
In the text, the author deals with various topics such as the materials of the strings used in the string instruments; the stringed instruments of native groups and used in orchestras and other characteristics of the stringed instruments. Due to the above, it can be affirmed that the central theme of this text is the string instruments. So the correct answer is D. Show how stringed instruments have several different characteristics.