A.
The bottom-up process is to break the whole (natural) language into bite-sized, abstract little pieces, and this would make learning to read difficult.
B.
The readers will simply become "word callers" who can read the words on the page but do not understand what they have read.
C.
With the bottom-up model, readers can read classical Chinese essays and pronounce all of the words that they are reading, but they may have no comprehension of what they have read.
D.
The readers will get the details of the reading materials.