The early civilizations of mohenjo-daro and harappa began around?
a.) 7500 b. c
b.) 10,000 b. c
c.) 2500 b. c
d.) 1000 b. c

The civilization of the Indus River at the Mohenjo - daro and Harappa begun around 2500 bc. Thus, the answer to the question above is letter C. The cities were built of fire-baked bricks. This activity denuded most of the country side and was one of the main reasons for the downfall they experienced. 

Primary sources are usually  more accurate and are written by someone who experienced it or witnessed it. secondary sources are those who heard of it after the fact that can lose details and or twist the event in a light that benefits them.