W. While studying chimps, Jane Goodall discovered that they were capable of making and using tools to gather food. Before her discovery, people believed that humans' ability to make tools was what separated them from animals.

X. Jane Goodall met anthropologist Dr. Louis Leakey in 1957. He was an important colleague for Jane Goodall. Dr. Leakey was the person who proposed a long-term study on wild chimpanzees. He thought that by observing first-hand the actions of chimps, scientists could understand more about human evolution.

Y. Jane, as a child, had a very good relationship with her mother. Their good relationship continued, even as Jane fought her way to Africa, when no one else said she could do it.

Z. Since I last wrote, an awful lot has happened. For one thing I have had a great deal of work, now happily disposed of into various files and envelopes. Friday was my nicest day in Kenya. Here in Nairobi is one of the best Natural History Museums there is, with all the most up-to-date and modern methods of showing and arrangements, etc. The curator, who is responsible for all this, is a man called Dr. Leakey.
Which of the paragraphs above most likely comes from a primary source?
A.
Y
B.
W
C.
Z
D.
X