Inferred you are referring to the article New math: Fail + try again = real learning by Susan Moran.
Answer:
B. Allowing and encouraging people to fail helps them to make sense of what they are learning.
Explanation:
Remember, we are told of the example of Thomas Edison who failed several times before inventing how new type of battery storage.
Also, the article says that learning from mistakes enables one develop an appreciation for how failure often leads to new discoveries and inventions. Noteworthy is the fact that the article mentions the word fail not less than 13 times indicating strong emphasis on the subject matter.