We need to find an answer choice that will explain why computer-assisted educational programs work well for students studying arithmetic, and yet are of little help in studying science and no help at all with reading and writing skills.
Answer choice (B) does just that. It explains that the exactness of arithmetic makes it the most suitable to computer-assisted education; so the computer assisted educational programs work best for those students studying for arithmetic and proportionately less well for subjects that are less "exact."
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