Even though you have posted the answer along with the question, I will confirm it and offer an explanation.
Answer:
What is meant by the phrase is:
B. She acts as though the cows are special in order to divert the children's attention.
Explanation:
In "The Story-Teller", a short story by author Saki, an aunt is traveling on a train carriage along with her nieces and nephew. Occupying the same carriage is a bachelor, who is constantly scowling because of the children's misbehavior. They are restless, constantly asking questions, moving around, smacking the cushions of the seats, and even reciting poems. To distract them and keep them quiet, the aunt calls the children to look out the window. The fields are full of cows, which only makes the children ask even more questions. All of a sudden:
"Oh, look at those cows!" exclaimed the aunt. Nearly every field along the line had contained cows or bullocks, but she spoke as though she were drawing attention to a rarity.
They had been seeing cows all along. But, to make them stop asking questions and divert their attention, the aunt tries to make the children believe there is something special about these cows. Of course, it does not work.
