单选题：Questionsare based on the following passage.Call it the "l

Questionsare based on the following passage.
Call it the "learning paradox" : the more you struggle and even fail while you're trying to learn new information, the better you're likely to recall and apply that information later.
The learning paradox is at the heart of "productive failure," a phenomenon identified by researcherManu Kapur. Kapur points out that while the model adopted by many teachers when introducing studentsto new knowledge--providing lots of structure and guidance.early on, until the student show that theycan do it on their own--makes intuitive sense, it may not be the best way to promote learning. Rather, it'sbetter to let the learners wrestle (较劲) with the material on their own for a while, refraining from givingthem any assistance at the start. In a paper published recently, Kapur applied the principle of productivefailure to mathematical problem solving in three schools.
With one group of students, the teacher provided strong"scaffolding"--instructional support--andfeedback. With the teacher's help, these pupils were able to find the answers to their set of problems,Meanwhile, a second group was directed to solve the same problems by collaborating with one another,without any prompts from their instructor. These students weren't able to complete the problems　correctly. But in the course of trying to do so, they generated a lot of ideas about the nature of theproblems and about what potential solutions would look like. And when the two groups were tested onwhat they'd learned, the second group "significantly outperformed" the first.
The apparent struggles of the floundering (挣扎的) group have what Kapur calls a "hidden efficacy":they lead people to understand the deep structure of problems, not simply their correct solutions. Whenthese students encounter a new problem of the same type on a test, they're able to transfer the knowledgethey've gathered more effectively than those who were the passive recipients of someone else's expertise.In the real world, problems rarely come neatly packaged, so being able to discern their deep structureis key. But, Kapur notes, none of us like to fail, no matter how often Silicon Valley entrepreneurs praisethe beneficial effects of an idea that fails or a start-up company that crashes and burns. So we need to"design for productive failure" by building it into the learning process. Kapur has identified threeconditions that promote this kind of beneficial struggle. First, choose problems to work on that "challengebut do not frustrate. " Second, provide learners with opportunities to explain and elaborate on whatthey're doing. Third, give learners the chance to compare and contrast good and bad solutions to theproblems. And to those students who protest this tough-love teaching style: you'll thank me later.

Why does the author call the learning process a paradox? A．Pains do not necessarily lead to gains.
B．What is learned is rarely applicable in life.
C．Failure more often than not breeds success.
D．The more is taught, the less is learnt.