It is important to a difficult chapter. a. memorize c. summarize b. read to the end d. none of these

The answer is b. "read to the end"
It makes intuitive sense and is the only solution that is correct in terms of the grammar. 

The three steps before modern english were indo-european, germanic, and old english. as peoples moved around the eurasian continent, their languages changed. throughout the ages, the languages became more specialized. as english has many germanic influences, it is easy to see how this was one of the forebears. also, old english was one of the main ancestors of the modern language, spoken in the 5th through about the 13th centuries.