Read the excerpt from sudanese slit drum.

it is another document of the enduring geopolitical fault-line around the nile cataracts that we have encountered twice before: in the sphinx of taharqo (chapter 22) and the head of augustus (chapter 35). this drum is part of the history of indigenous african culture, of the east african slave trade centred on khartoum, and of the european scramble for africa at the end of the nineteenth century.

since the passage shows how macgregor perceives and discusses the topic of the sudanese slit drum, it is an example of a

a. viewpoint.
b. summary.
c. source.
d. detail.