A、The spelling and meaning of words. B、The general meaning of the text. C、The exact shape and order of letters. D、The details of

(16)There is no doubt that adults, and even highly educated adults, vary greatly in the speed and efficiency of their reading. Some proceed very slowly throughout; others dash along too quickly and then have to re-read. Poor readers in particular may lack the ability to vary their manner of reading according to the type of reading matter and to their intentions in reading it.
     (17)A good reader can move at great speed through the text of a novel or similar light reading matter. He may be able to skim a page, picking up a word or two here and there, and gain a general idea of what the text is about without really reading it. In reading more difficult material, with the intention of taking in the whole of it, he will proceed more slowly, but even then he will vary his pace, concentrating on the key words and passages, perhaps re-reading them several times and pass more quickly over the remainder.
     (18)A type of reading which necessitates careful attention to detail is proofreading, in which the reader, in order to detect misprints in a sample print, has to notice not so much the meaning of what he reads as the exact shape and order of letters and words in the text. This is extremely difficult for most people, since they are accustomed to overlooking such details. In fact, proofreading can be done only by reading very slowly, and by paying comparatively little attention to the general meaning of the text.
16. In what aspects do adults differ when doing their reading?
17. What would a good reader do when reading a novel?
18. What would be focused on in proofreading?