The correct option is D all of the above reasons
In the passage, the author clearly states that learning is a painful process because it exposes our ignorance, our views and hypothesis are challenged and it also involves criticizing the views of others. This makes option D as the apt choice.
Refer to this line to identify the answer: A learning space needs to be hospitable not to make learning painless, but to make painful things possible, things without which no learning can occur-things like exposing ignorance, testing tentative hypotheses, challenging false or partial information, and mutual criticism of thought.