Source is author can use to research and develop ideas in an informational text.
a: autobiographical paper
b: outside publication
c: personal opinion
d: social network

According to the excerpt above, the correct answer to fullfil the incomplete sentence is letter B. “Source is an outside publication that an author can use to research and develop ideas in an informational text”. A source can be any specific publication or other type of media where specific information was obtained. These are usually included in footnotes, endnotes or any other bibliographical text; and also can be people.

the reason that neiterkob's daughter most likely tell the beginnings of the maasai is : to explain the readers the origin of maasai culture

with this explanation, the reader will grasp a better concept about it and not lost in the middle of reading.

                                            (hope this )

"urban sprawl, the spreading of large developments of housing and shopping areas around a city’s center, has many negative cultural and environmental effects. " (from your link)

so, your answer is: it has a negative effect on the environment, otherwise known as c~hope this mate.