What can we learn about the puzzle? ( )

参考解析：

细节题。题干问：对这个工资之谜的说法，哪一个是正确的。根据第一段when demand for something goes up, so does its costs. So, many economists wonder why today’s high demand for workers hasn’t translated into bigger increases in pay. 可知，A选项，这个谜跟劳动力短缺与工资停滞有关。所以A是正确的。根据第一段It isn’t just, for example, that productivity has slowed, making it harder for businesses to justify paying more – though that is certainly a factor. At 4 percent, unemployment has been very low. Businesses report having a hard time finding available workers.可知，B选项，它与低失业率几乎没有关系。原文说不仅仅跟生产力下降有关，还跟低失业率有关，故排除B；C选项，这主要是由生产力下降造成的。从It isn’t just, for example, that productivity has slowed, making it harder for businesses to justify paying more – though that is certainly a factor 可看出，C项说生产力下降是主要原因并不准确，故排除；D选项，许多经济学家来对此知之甚少。这个说法，在文中，并无事实依据。故本题正确答案选A。