Question

passage
every day is a curly hair day for sheep. those curls are part of what makes woolen sweaters so cozy—the maze of fibers helps trap warm air, keeping it close to the body. but wrapped up in those curls may also be answers to a longstanding mystery: exactly how a strand of hair winds itself into a curl on the cellular level.
for many years, there were two competing theories to explain what makes hairs curl in sheep. research by scientists in new zealand and japan published in the journal of experimental biology finds that neither theory is exactly correct. but it remains likely that differences between certain cells on a hair may explain what makes a sheeps wool curly. and while human hair has some crucial differences from wool, understanding why curls happen in one mammals hair could eventually shed light on others, including ours.
adapted from veronique greenwood, \what makes some hair curly? not quite what scientists thought.\ ©2018 by the new york times company.
question
in context, the main purpose of the second paragraph is to
disprove a long - held theory that differences between certain cells are what cause sheeps wool to curl
describe the research methodology used by scientists to study why sheeps wool is curly
illustrate why certain cellular differences among mammal species make it hard to definitively explain the cause of curly hair
introduce a research study that has furthered scientists understanding of why hair curls

Explanation:

The second paragraph starts by mentioning two competing theories about sheep's curly hair. Then it says research finds neither is exactly correct but that differences in cells might explain it. Also, it hints that understanding sheep's hair could help with human hair. This shows the paragraph is introducing a research study (the one from New Zealand and Japan scientists) that advances the understanding of why hair curls.

• The first option is wrong because the paragraph says "it remains likely that differences between certain cells...", so it doesn't disprove the cell - difference theory.
• The second option is incorrect as there is no mention of research methodology (like how the experiments were set up, sample size, etc.).
• The third option is off - topic. The paragraph is mainly about sheep's hair and its relation to understanding other mammals' hair (including humans), not about differences among mammal species making it hard to explain curly hair.

Answer:

introduce a research study that has furthered scientists’ understanding of why hair curls