Final answer:
The length of written work does not affect the ability to read and understand material. Factors that impact understanding include visual skill, purpose for reading, and vocabulary knowledge.
Step-by-step explanation:
To answer your question, the factor that does not affect your ability to read and understand material is (a) length of written work. While the length can influence the time it takes to read something, it does not inherently affect the understanding of the material itself. Instead, one's understanding is more directly impacted by (b) visual skill, which includes the ability to see and interpret written text; (c) purpose for reading, which influences the approach to and engagement with the text; and (d) extent of vocabulary, as familiarity with words used in the written work allows for better comprehension.
Having a clear purpose for reading sets the context in which you approach the material and can greatly impact your focus and retention of information. Visual skill is necessary for the basic decoding of words and sentences, and vocabulary knowledge helps make sense of complex sentences and concepts within the text.