Which chinese sailor began a series of seven naval expeditions that went as far as te east coast of africa?
a. mongke
b. zheng he
c. berke
d. hulegu

The Chinese sailor who began those expeditions was "B" Zheng he.

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.