The correct option is B first two
The underlined phrase is incorrect, it needs to be changed because there can only be one first, there can't be two firsts hence option A is incorrect. Same goes with option B, initial means beginning, there can't be two beginnings of a book. Option C is correct as the phrase "first two" means the first and the second when we use 'first' we can combine it with a number to refer to that number of chapters from the beginning of the book. Option D is incorrect because there can't be two parts to a first. 'First' refers to the very beginning chapter of the book, it's singular and there can't be 'two' of something that's only one and it wouldn't fit the context of the given sentence.