Answer: B mothers instinctively know how to cradle their babies in a comforting way.
Step-by-step explanation:
It is explained that mothers all over the world do this. Since it is unlikely so many people from so many different cultures teach the same thing, we can assume its instinct. Plus, looking at the other answers you can tell they are obviosly wrong. A is wrong because the passage says nothing about being taught and C is wrong because the passage does not mention fathers.