What can be inferred from the passage a.

问题：

What can be inferred from the passage a. There is no obvious reason for the unbalanced distribution of dyslexia in the world. b. The existing theories about dyslexia are solid and conclusive. c. There are underlying reasons for the differences with dyslexic problems with different peoples. d. The relatively lower number of its people suffering from dyslexia in Japan may be attributed to its reading and writing system.