It is good idea to increase your reading speed while

A. Reading simple naterial

B. Reading unnecessary examples

C. Reading restatements

D. All of these

The answer is D all the above

I would say D because if the material is simple, there is no need to spend alot of time reading it, if the examples are unnecessary then again no need to spend time reading it, and if something is restated then you already know what it is meaning so you can increase your reading speed in all these circumstances.