The answer is D. India developed and maintained a securely centralized and powerful empire that lasted for centuries.
Advantages: Primary sources directly address your topic and often provide information that is unavailable elsewhere. For example, the questions you compose for an interview or a survey will likely target your unique interest in the topic. Similarly, to test a particular hypothesis, you can design your own experiment.
Disadvantages: Some primary sources, such as eyewitness accounts, may be too close to the subject, lacking a critical distance. Others, such as interviews, surveys, and experiments, are time consuming to prepare, administer, and analyze. Finally, unless you have been trained in accepted methodologies, your own primary research in certain fields of study may not be recognized as valid.
